The detoxifying properties of cruciferous vegetables components have been the subject of several recent investigations. Evidences from many biochemical and pharmacological studies indicated that higher consumption of cruciferous vegetables is associated with lower incidence of harmful actions such as hepatotoxicity and oxidative stress in animal and human populations. Recently, it has been reported that drug metabolizing and detoxifying enzyme activities were increased by cruciferous vegetable extract in which sinigrin is known to be a main active component, accounting for about 2 to 3 percents of total extract. The detoxifying effect of sinigrin has been well reported in several literatures. The metabolism of sinigrin in animal, however, has not been reported yet. That led us to study the metabolism of sinigrin in rat. Sinigrin is nown to be metabolized into three compounds, i.e., allyl isothiocyanate, glucose and potassium phosphate in cruciferous vegetables. Allyl isothiocyanate was formed in rat hepatic mitochondrial fraction in dose and incubation time dependent manner, that was confirmed by HPLC. Glucose formation was came up with results similar to that of allyl isothiocyanate. Three hours after i.p. administration of sinigrin to rat, allyl isothiocyanate appeared in rat liver, and five hours later it was detected in liver and blood. The above results suggested that sinigrin might be metabolized into allyl isothiocyanate, glucose and potassium phosphate in rat.