Synthesis of spiothiohydantoin derivatives of hydantocidin is described. The key feature of the synthesis was spirothiohydantoin ring formation through an iminophosphorane intermediate. Spirothiohydantoin derivative 2 maintained comparable herbicidal activity to that of the natural compound except against fall panicum, when applied through a foliage of weeds at 1000 ppm. Surprisingly, its epimer 15 also demonstrated good herbicidal activity under the same condition, while 5-epi-hydantocidin 16 displayed fair activity.