In order to develop an efficient method for producing thiamin-rich esculent yeast using rice bran, the optimum condition for thiamin accumulation from rice bran extract by bakers' yeast was investigated. The optimum pH and temperature were the same as those for accumulation from aqueous thiamin hydrochloride solution, and the process involved was considered to be active transport, as in the case of accumulation from aqueous solution. It was considered that sucrose contained in the rice bran extract served as an energy source for the transport. However, results of reaction kinetic experiments indicated that substances present in rice bran extract caused complex promotive and inhibitory effects on the accumulation. It was found that the velocity of thiamin accumulation could be improved by preincubation of the yeast and/or preheating of the rice bran extract.