We report the discovery of the partially eclipsing binary LP 133-373 .
Nearly identical eclipses along with observed photometric colors and spectroscopy indicate that it is a pair of chromospherically active dM4 stars in a circular 1.6 d orbit .
Light and velocity curve modeling to our differential photometry and velocity data show that each star has a mass and radius of 0.340 \pm 0.014 M _ { \odot } and 0.33 \pm 0.02 R _ { \odot } .
The binary is itself part of a common proper motion pair with LP 133-374 a cool DC or possible DA white dwarf with a mass of 0.49 - 0.82 M _ { \odot } , which would make the system at least 3 Gyr old .