
The file extension Of MS Access has been changing following the years and the software version. The very first Access version is Access 1.1. Up until Access 2003, the past versions are considered to be legacy version. The most popular Ms. Access extension are .accdb and .mdb. There .accdb file format is come from the Ms Access 2007 version and later. Meanwhile, the .mdb extension is the format from 2003 version and earlier. The popularity of .mdb version is because some people still using Access 2003 version even through it is legacy.

(The comparison of the file version icon)
Aside of the 2 formats, there are some of popular extension as listed in table below.
Current Extension (2007, 2010, 2013, 2016)
Access Blank Project Template | .adn |
Access Database | .accdb |
Access Database Runtime | .accdr |
Access Database Template | .accdt |
Access Add-In | .accda |
Access Workgroup | .mdw |
Protected Access Database | .accde |
Legacy Extension (2003 and earlier)
Access Database | .mdb |
Access Blank Database Template | .mdn |
Access Add-in Data | .mdt |
Access Data Project | .adp |
Protected Access Database | .mde |
With the different extension, the latest (2007 and later) version can open most of the legacy file types, but not all. Most of the newest version still can open or save the database into .mdb file format. Like most of the software, the early 2003 version cannot open the newest .accdb extension. However, the problems may still occur due to different extension and version. The most common one is inability to save or convert the .accdb to .mdb files because of the recent features that not supported by the older version.

In some cases, you may still able to convert the .accdb into .mdb, but with risk to lost some of the newest feature. This may cause the database to not work improperly or worse, corrupted database.
Note: To convert database, go to save as and choose the .mdb extension in format.

(Saving Access Database in another file format)
Aside of the different extension, sometimes same extension may still cause error if it opened in different Access version. One of the error is Unrecognized Database Format, which you can read further and solved in Unrecognized Database Format.
Related Access Database
- example2013 accdb
- file extension version