Cubane-like heteronuclear transition-metal clusters (n-Bu(4)N)(3)[WCu3Br4S4] (I) and (n-Bu(4)N)(3)[WAg3Br4S4) (II) were synthesized by solid-state reactions. These molecules respond nonlinearly to the incident light and exhibit a strong optical limiting effect with threshold and transmitted saturation levels of 1.6 and 0.7 J/cm(2) for compound I and 0.8 and 0.5 J/cm(2) for compound II, as examined in a l-mm cell with 7-ns laser pulses at 532 nm. The optical limiting power of compound I is comparable to that of C-60 while the optical limiting power of compound II is about 2 times stronger than that of C-60, one of the best molecules reported for optical limiting.