We have investigated the magnetic and magneto-optic properties of epitaxial-tau MnAl/AlAs/GaAs heterostructures grown by molecular beam epitaxy. The ferromagnetic-tau phase of MnAl was observed, and perpendicular anisotropy was confirmed by the nearly square hysteresis loops. The polar magneto-optic Kerr rotation of thin 10 nm tau MnAl films is nearly constant at 0.11-degrees from 220 to 820 nm.