The EXT file system (short for Extended File System) and it’s family members of EXT2, EXT3, and EXT4, are the file systems used by Linux. Mac users who work with multiple platforms may notice that OS X is unable to mount EXT partitions on its own, and thus anyone wishing to mount and read EXT drives and other file systems will need to rely on a third party utility.

OSXFuse is one such tool, a free open source offering that allows OS X to read EXT volumes, and if you’re comfortable with some uncertainty and risk to the Linux partition, you can even enable an experimental EXT write function too.

Full article here:
How to Mount EXT4 Linux File Systems on a Mac with OS X Fuse (OS X Daily)