Information relevant to this issue has been incorporated into the documentation as of Release 2013a (R2013a). For previous releases, read below for any additional information:
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 by right click on the windows icon on the bottom left corner of your screen then select 'Control Panel'
2. In the ‘Control Panel’, click on 'Programs' section, then on the next page, under the 'Default Programs', click on 'Make a file type always open in a specific program'
3. In the next page, you will see a list of file extensions with their associated default programs. Find the MAT file then click 'Change program' button at the top right corner
4. 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.
or follow the instructions from the following link: