Download the files matfilerw.jar and openmat_.jar from the Assets section in the recent release. Copy matfilerw.jar to the jars subdirectory of your Fiji installation and openmat_.jar to the Plugins subdirectory of Fiji.

Click the menu File > Open > Mat to open your matlab mat files.

This plugin is knitted around the matfilerw library.

It is in experimental stage and I would be happy about user feedback. Drop me a line (rhaase at mpi-cbg.de) if you want to support its development - either by providing feedback or by coding :-)