1) Weanling rats were individually administered vitamin E orally 0.5_??_0.75mg/day/rat (control group), 5.0_??_7.5mg/day/rat (×10 group) and 50_??_75mg/day/rat (×100 group). Period of experimental group was 12 wk. Increase in body wt. of weanling rats was low in the 50_??_75mg/day/rat (×100 group) and wt. of the adrenal gland, thymus, thyroid and testis did not vary among the subjects. 2) Mother rats were fed on the same diets as the said experimental 2 groups of vitamin E for about 20 days before pregnancy and then through gestation and the natal period. Their offspring were fed on a normal diet during 12 wk. after weaning. Increase in body wt. of weanling rats did not differ nor were abnormalities observed in the organs. 3) Mother rats were fed on the same experimental method of vitamin E through gestation, natal and lactation periods. Their offspring were fed on a normal diet during 12 wk. after weaning. Increase in body wt. of the weanling rats did not differ among the three groups nor were there abnormalities observed in the organs. 4) Mother rats and their weanlings fed on a 75mg/day/rat diet, the former for about 20 days before pregnancy and through gestation period, the latter during 12 wk. after weaning, were normal as to the number of RBC and WBC, the value of haematocrit and hemoglobin, bleeding time and prothrombin time and blood sugar and creatin urea. 5) From the viewpoint of development pharmacology, it may be concluded that vitamin E is a comparatively safe drug.