Triplet state nonlinearity ofC60in toluene is studied using theZ-scan technique with 8 ns, 532 nm pulses from aQ-switched Nd:YAG laser. Compared with theZ-scan results ofC60in toluene and iodine in toluene with proper concentration, the solvent instantaneous nonlinearity and the thermal nonlinearity resulting from theC60intersystem crossing and excited state absorption are estimated. The real part of theC60triplet state molecular polarizability is obtained. ©1997 American Institute of Physics.