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How To Update Galaxy S3 I9300 to AOSP Android 6.0 Marshmallow Custom ROM

Samsung is not going to release the latest Android OS firmware OTA updates for their old flagship smartphone, Galaxy S3 but being an Galaxy S3 I9300 user you’ll be happy to know that you can still experience the latest Android 6.0 Marshmallow firmware on your phone. Thanks to the XDA developers for providing a custom ROM which is ported from the stock Android Marshmallow firmware. This AOSP ROM is not enough stable and it can’t be used as a daily driver yet but the developers are working hard to fix the bugs. The AOSP Android 6.0 Marshmallow ROM brings a pure Android UI and there are no Samsung branded features, processes and apps like TouchWiz pre-installed, means its a bloatware free firmware. So you can enjoy your Galaxy S3 with enhanced faster performance with an upgraded battery life after getting this Nexus-like experience.

Keep in mind that this ROM is not developed by Samsung and is currently under development thus you might face some minor bugs or not functioning features. You can read more about this ROM and users who have already tested this AOSP Marshmallow ROM on their Galaxy S3 devices, found it working fine. All you need to have the latest version of a custom recovery like CWM or TWRP already installed on your S3 in order to flash the ROM and Google Apps .zip files as well as have a root access on your Galaxy S3 because you cannot flash a custom ROM on your phone without having root access. So it is important that the Galaxy S3 must be rooted before installing this Android 6.0 Marshmallow firmware.

Installing Android 6.0 Marshmallow on Galaxy S3 via AOSP Custom ROM


This guide containing AOSP Android 6.0 Marshmallow custom ROM can be used for the Galaxy S3 I9300 model only. Do not try to install this firmware on any other device or incorrect variant.


AndroidBlog will not be held responsible for any kind of damage occurred to your Galaxy S3 I9300 during or after the installation of this AOSP Android 6.0 Marshmallow custom ROM. You will lose the warranty of your device by flashing this software. Proceed at your own risk.


  • Take a complete backup of all your data and setting on your phone like contacts, call logs, SMS, MMS, internet settings, installed apps, photos and audio/videos files etc.
  • Turn OFF the Antivirus and other security features from your computer to avoid unexpected issues while downloading the firmware and installation.
  • Download and install Samsung USB Drivers on your PC.
  • Enable USB Debugging option on your Galaxy S3 by navigating to Settings – Developer Options.
    • (Note:- Go to Settings – About Phone and tap on Built Number for a few times to enable Developer Options)
  • The battery level of your Galaxy S3 should be at least about 70% before proceeding to the installation guide.

Required Files:

Steps to Install Android 6.0 Marshmallow on Galaxy S3 I9300 with AOSP Custom ROM:

1:- First, download the AOSP Android 6.0 Marshmallow custom ROM ( from the above links on the desktop of your PC. (Do not extract)

2:- Now connect your Galaxy S3 to PC using its USB data cable and mount the Memory Storage of the phone.

3:- Copy/paste the AOSP Android 6.0 Marshmallow .zip file to the root folder of your SD Card on the phone.

4:- Disconnect the device from the PC and turn it off in order to boot into Recovery Mode.

5:- Turn on the phone by pressing and holding Volume Up + Home + Power keys at the same time for a few seconds.

6:- While your device is now recovery mode, perform a full data wipe by selecting wipe data/factory reset, wipe cache partition and wipe dalvik cache.

Note:- Wipe Dalvik Cache will help you to prevent boot loops and issues related to ROM while installation.

7:- Next, navigate to the main menu of Recovery and choose install zip from sdcard > choose zip from sdcard. Find the ROM .zip file that you’ve already transferred to the SD Card of your phone in Step No 3. Just select it and confirm the installation of AOSP Android 6.0 Marshmallow ROM file to begin.

8:- Install Google Apps Package by repeating the above steps on your Galaxy S3.

9:- After flashing the ROM on the phone successfully, reboot it by selecting reboot system now.

Your device may take some time to boot for the first time after the installation. So be patient and wait for the process to be completed.

Done! You’ve successfully installed the Android 6.0 Marshmallow Custom ROM on Galaxy S3 I9300.

Let us know in the comments area below if you have any issue or question regarding the above step-by-step guide.

Aamir Jamal

An Android Geek and audiophile who love to read and write reviews/tutorials about gadgets and new tech stuff. He has written 1007 guides and other posts.

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