diff --git a/mod/chat/classes/external.php b/mod/chat/classes/external.php
index 8bb4b15a979..0ef65660cd3 100644
--- a/mod/chat/classes/external.php
+++ b/mod/chat/classes/external.php
@@ -29,6 +29,8 @@ defined('MOODLE_INTERNAL') || die;
 require_once($CFG->libdir . '/externallib.php');
 require_once($CFG->dirroot . '/mod/chat/lib.php');
 
+use mod_chat\external\chat_message_exporter;
+
 /**
  * Chat external functions
  *
@@ -735,4 +737,108 @@ class mod_chat_external extends external_api {
             )
         );
     }
+
+    /**
+     * Returns description of method parameters
+     *
+     * @return external_function_parameters
+     * @since Moodle 3.4
+     */
+    public static function get_session_messages_parameters() {
+        return new external_function_parameters(
+            array(
+                'chatid' => new external_value(PARAM_INT, 'Chat instance id.'),
+                'sessionstart' => new external_value(PARAM_INT, 'The session start time (timestamp).'),
+                'sessionend' => new external_value(PARAM_INT, 'The session end time (timestamp).'),
+                'groupid' => new external_value(PARAM_INT, 'Get messages from users in this group.
+                                                0 means that the function will determine the user group', VALUE_DEFAULT, 0),
+            )
+        );
+    }
+
+    /**
+     * Retrieves messages of the given chat session.
+     *
+     * @param int $chatid the chat instance id
+     * @param int $sessionstart the session start time (timestamp)
+     * @param int $sessionend the session end time (timestamp)
+     * @param int $groupid filter messages by this group. 0 to determine the group.
+     * @return array of warnings and the messages
+     * @since Moodle 3.4
+     * @throws moodle_exception
+     */
+    public static function get_session_messages($chatid, $sessionstart, $sessionend, $groupid = 0) {
+        global $DB, $PAGE;
+
+        $params = self::validate_parameters(self::get_session_messages_parameters(),
+                                            array(
+                                                'chatid' => $chatid,
+                                                'sessionstart' => $sessionstart,
+                                                'sessionend' => $sessionend,
+                                                'groupid' => $groupid,
+                                            ));
+        $messages = $warnings = array();
+
+        // Request and permission validation.
+        $chat = $DB->get_record('chat', array('id' => $params['chatid']), '*', MUST_EXIST);
+        list($course, $cm) = get_course_and_cm_from_instance($chat, 'chat');
+
+        $context = context_module::instance($cm->id);
+        self::validate_context($context);
+
+        if (empty($chat->studentlogs) && !has_capability('mod/chat:readlog', $context)) {
+            throw new moodle_exception('nopermissiontoseethechatlog', 'chat');
+        }
+
+        if (!empty($params['groupid'])) {
+            $groupid = $params['groupid'];
+            // Determine is the group is visible to user.
+            if (!groups_group_visible($groupid, $course, $cm)) {
+                throw new moodle_exception('notingroup');
+            }
+        } else {
+            // Check to see if groups are being used here.
+            if ($groupmode = groups_get_activity_groupmode($cm)) {
+                $groupid = groups_get_activity_group($cm);
+                // Determine is the group is visible to user (this is particullary for the group 0).
+                if (!groups_group_visible($groupid, $course, $cm)) {
+                    throw new moodle_exception('notingroup');
+                }
+            } else {
+                $groupid = 0;
+            }
+        }
+
+        $messages = chat_get_session_messages($chat->id, $groupid, $params['sessionstart'], $params['sessionend'],
+            'timestamp ASC');
+        if ($messages) {
+            foreach ($messages as $message) {
+                $exporter = new chat_message_exporter($message, array('context' => $context));
+                $returneditems[] = $exporter->export($PAGE->get_renderer('core'));
+            }
+        }
+
+        $result = array(
+            'messages' => $messages,
+            'warnings' => $warnings,
+        );
+        return $result;
+    }
+
+    /**
+     * Returns description of method result value
+     *
+     * @return external_description
+     * @since Moodle 3.4
+     */
+    public static function get_session_messages_returns() {
+        return new external_single_structure(
+            array(
+                'messages' => new external_multiple_structure(
+                    chat_message_exporter::get_read_structure()
+                ),
+                'warnings' => new external_warnings()
+            )
+        );
+    }
 }
diff --git a/mod/chat/classes/external/chat_message_exporter.php b/mod/chat/classes/external/chat_message_exporter.php
new file mode 100644
index 00000000000..1f3cac48b67
--- /dev/null
+++ b/mod/chat/classes/external/chat_message_exporter.php
@@ -0,0 +1,101 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Class for exporting a chat message.
+ *
+ * @package    mod_chat
+ * @copyright  2017 Juan Leyva <juan@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+namespace mod_chat\external;
+defined('MOODLE_INTERNAL') || die();
+
+use core\external\exporter;
+
+/**
+ * Class for exporting a chat message.
+ *
+ * @copyright  2017 Juan Leyva <juan@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class chat_message_exporter extends exporter {
+
+    /**
+     * Defines exporter properties.
+     *
+     * @return array
+     */
+    protected static function define_properties() {
+        return array(
+            'id' => array(
+                'type' => PARAM_INT,
+                'description' => 'The message record id.',
+            ),
+            'chatid' => array(
+                'type' => PARAM_INT,
+                'description' => 'The chat id.',
+                'default' => 0,
+            ),
+            'userid' => array(
+                'type' => PARAM_INT,
+                'description' => 'The user who wrote the message.',
+                'default' => 0,
+            ),
+            'groupid' => array(
+                'type' => PARAM_INT,
+                'description' => 'The group this message belongs to.',
+                'default' => 0,
+            ),
+            'issystem' => array(
+                'type' => PARAM_BOOL,
+                'description' => 'Whether is a system message or not.',
+                'default' => false,
+            ),
+            'message' => array(
+                'type' => PARAM_RAW,
+                'description' => 'The message text.',
+            ),
+            'timestamp' => array(
+                'type' => PARAM_INT,
+                'description' => 'The message timestamp (indicates when the message was sent).',
+                'default' => 0,
+            ),
+        );
+    }
+
+    /**
+     * Defines related information.
+     *
+     * @return array
+     */
+    protected static function define_related() {
+        return array(
+            'context' => 'context',
+        );
+    }
+
+    /**
+     * Get the formatting parameters for the name.
+     *
+     * @return array
+     */
+    protected function get_format_parameters_for_message() {
+        return [
+            'component' => 'mod_chat',
+        ];
+    }
+}
diff --git a/mod/chat/db/services.php b/mod/chat/db/services.php
index dcc0897b8f5..6bbd9289600 100644
--- a/mod/chat/db/services.php
+++ b/mod/chat/db/services.php
@@ -88,5 +88,12 @@ $functions = array(
         'description'   => 'Retrieves chat sessions for a given chat.',
         'type'          => 'read',
         'services'      => array(MOODLE_OFFICIAL_MOBILE_SERVICE)
-    )
+    ),
+    'mod_chat_get_session_messages' => array(
+        'classname'     => 'mod_chat_external',
+        'methodname'    => 'get_session_messages',
+        'description'   => 'Retrieves messages of the given chat session.',
+        'type'          => 'read',
+        'services'      => array(MOODLE_OFFICIAL_MOBILE_SERVICE)
+    ),
 );
diff --git a/mod/chat/tests/externallib_test.php b/mod/chat/tests/externallib_test.php
index cf86bb896db..2443f71d6b1 100644
--- a/mod/chat/tests/externallib_test.php
+++ b/mod/chat/tests/externallib_test.php
@@ -431,4 +431,65 @@ class mod_chat_external_testcase extends externallib_advanced_testcase {
         $this->assertEquals($timenow - HOURSECS + 70, $result['sessions'][0]['sessionstart']);  // First not system message time.
         $this->assertEmpty($result['warnings']);
     }
+
+    /**
+     * Test get_session_messages
+     */
+    public function test_get_session_messages() {
+        global $DB;
+
+        $this->resetAfterTest(true);
+
+        // Setup test data.
+        $this->setAdminUser();
+        $course = $this->getDataGenerator()->create_course();
+        $chat = $this->getDataGenerator()->create_module('chat', array('course' => $course->id));
+
+        $user1 = self::getDataGenerator()->create_user();
+        $user2 = self::getDataGenerator()->create_user();
+        $studentrole = $DB->get_record('role', array('shortname' => 'student'));
+        $this->getDataGenerator()->enrol_user($user1->id, $course->id, $studentrole->id);
+        $this->getDataGenerator()->enrol_user($user2->id, $course->id, $studentrole->id);
+
+        // Start a chat and send a few messages.
+        $this->setUser($user1);
+        $result = mod_chat_external::login_user($chat->id);
+        $result = external_api::clean_returnvalue(mod_chat_external::login_user_returns(), $result);
+        $chatsid = $result['chatsid'];
+        mod_chat_external::send_chat_message($chatsid, 'hello!');
+        mod_chat_external::send_chat_message($chatsid, 'bye bye!');
+
+        $this->setUser($user2);
+        $result = mod_chat_external::login_user($chat->id);
+        $result = external_api::clean_returnvalue(mod_chat_external::login_user_returns(), $result);
+        $chatsid = $result['chatsid'];
+        mod_chat_external::send_chat_message($chatsid, 'greetings!');
+
+        // Pass showall parameter to indicate that we want not completed sessions.
+        $result = mod_chat_external::get_sessions($chat->id, 0, true);
+        $result = external_api::clean_returnvalue(mod_chat_external::get_sessions_returns(), $result);
+        $this->assertCount(1, $result['sessions']); // One session.
+
+        $sessionstart = $result['sessions'][0]['sessionstart'];
+        $sessionend = $result['sessions'][0]['sessionend'];
+        $result = mod_chat_external::get_session_messages($chat->id, $sessionstart, $sessionend);
+        $result = external_api::clean_returnvalue(mod_chat_external::get_session_messages_returns(), $result);
+        $this->assertCount(5, $result['messages']); // 2 system + 3 personal messages.
+        $found = 0;
+        foreach ($result['messages'] as $message) {
+            if (!$message['issystem']) {
+                if ($message['userid'] == $user1->id) {
+                    if ($message['message'] != 'hello!') {
+                        $this->assertEquals('bye bye!', $message['message']);
+                        $found++;
+                    }
+                } else {
+                    $this->assertEquals($user2->id, $message['userid']);
+                    $this->assertEquals('greetings!', $message['message']);
+                    $found++;
+                }
+            }
+        }
+        $this->assertEquals(2, $found);
+    }
 }
diff --git a/mod/chat/version.php b/mod/chat/version.php
index 0486c4031f7..c313d4adde0 100644
--- a/mod/chat/version.php
+++ b/mod/chat/version.php
@@ -24,7 +24,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version   = 2017111302; // The current module version (Date: YYYYMMDDXX).
+$plugin->version   = 2017111303; // The current module version (Date: YYYYMMDDXX).
 $plugin->requires  = 2017110800; // Requires this Moodle version.
 $plugin->component = 'mod_chat'; // Full name of the plugin (used for diagnostics).
 $plugin->cron      = 300;