The clinical symptoms of thiamine deficiency, such as growth, change of fur, movement, paralysis of extrimities, and also several enzymatic activities of tissues were compared for rats, fed with 3 types of thiamine deficient diet, i. e., polished rice only, supplemented with lysine and threonine, and with casein. The group of rice diet showed severe signs of thiamine deficiency earlier than those of amino acid-supplemented group. The activity of xanthine oxidase, aldolase and transketolase of the tissues decreased markedly in the former, suggesting that the inadequate composition of amino acids in the diet may accelarate the fall of several enzymatic activities relating to the thiamine deficiency. These results suggest that the high incidence of thiamine deficiency among rice-eating peoples relates in some part with the inadequacy of amino acids of their diets.