We report millimeter-wave magneto-optical measurements on the high-spin molecule, Cr10 (OMe) 20 (O2 CCMe3) 10. The dependence of the electron paramagnetic resonance as a function of orientation and temperature demonstrates that this compound behaves as a single molecule magnet, and exhibits one of the smallest zero-field splittings (D=-0.045±0.004 K) yet reported for such a system. © 2005 American Institute of Physics.