Information relevant to this issue can be found in the documentation at the following link:
This behavior occurs after installing Microsoft Office. The .mat extension becomes associated with Microsoft Access if you do not deselect this option during Access installation.
Microsoft Office causes the *.mat files to appear as shortcuts and not as actual files to Windows.
If you are using Microsoft Windows 10, you can restore the file associations with the following steps:
1. Open 'Control Panel'. This can be done most easily from the Start menu or by searching for it
2. In the ‘Control Panel’, click on 'Programs' section, then on the next page, click 'Default Programs'
3. Click on 'Associate a file type or protocol with a program' then scroll down and click on 'Choose default apps by file type'
4. On the next page, you will see a list of file extensions with their associated default programs. Find the MAT file extension then click on either the plus sign or the current associated application to its right.
5. There will be a pop-up menu where you can select to associate the MAT file with MATLAB
If you are using Microsoft Windows Vista or 7, you can restore the file associations with the following steps:
1. Click the Windows Start menu.
2. Select Control Panel.
3a. If the Control Panel view is set to "View by: Category" in the top right, navigate to: Programs > Default Programs >Associate a file type or protocol with a program
3b. If the Control Panel view is set to "View by: Small icons" or "View by: Large icons" in the top right, navigate to: Default Programs >Associate a file type or protocol with a program
4. After the Set Associations window populates, scroll down to the .mat option.
5. Click it, and then click on "Change Program" on the top right corner.
6. Select MATLAB. If MATLAB is not listed in the program list, click on "Browse" then search for the MATLAB application, which is located in the MATLABROOT folder. On a Windows machine, this is usually C:\Program Files\MATLAB\R20* where R20* is the version of MATLAB.
7. Click Close to close the Set Associations window.
8. All MAT files will now open with MATLAB.
If you are using MATLAB on Microsoft Windows XP, read below for instructions:
1. From a Windows Explorer window, select "Tools -> Folder Options -> File Types".
2. Now select 'New'.
3. Enter the MAT extension in the text box.
4. Click 'Advanced' and from the List Box select 'MATLAB data file' or 'MATLAB MAT-file'.
5. After making this change, you will be able to use the "Change" button on the File Types dialog to make further changes such as selecting a specific MATLAB release.