Many reports have been published about the inferior quality of the oils extracted from rice bran which has been stored for long period than that from new rice bran owing to the rise in the acid value of the oil contained in rice bran during the storage.The work on the exposure of rice bran to gamma irradiation before the oil extraction was attempted to know if the treatment would be effective to control the rise of the acid value. Acid value of 35 was obtained for the rice oil extracted from rice bran that had been exposed to 7×106 rad of gamma irradiation from a Co60 source at our laboratory, whereas the value of the rice oil from unirradiated bran was 60.There was no significant difference between two groups of the oils as to the growth rate of mice given oral administration during three months.