The absorption and excretion of cyclocarbothiamine (CCT) were investigated when it was administered orally for human and rat. After oral administration of CCT for healthy subjects, the blood level and urinary excretion of thiamine were markedly higher as in case of the other modified thiamine derivatives than those of thiamine hydrochloride. When CCT was given to rat, the thiamine values of blood, liver, kidney and muscle were markedly elevated and it was observed that the phosphorylation of thiamine is also increased.