Abstract: This experiment was conducted with virgin wistar female rats. The body weight of the female rats was 195～339 g, that of the males was 285～373 g. The males and females were allowed to mate over-night at a ratio of 3:1. Then the pregnant rats were divided into groups (see table 1 and 2). Bis-A-TDA was given orally on various days.The rats were killed on day-20 of gestation so as to count the number of corpora lutea, implantation sites and live fetuses. The living fetuses were removed, weighed, inspected for gross abnormalities and sexes; the internaland skeletal malformations Of live fetuses were examined by Wilson's method.The following results wereobtained:1. If one dose is given, the most suitable time is to give the drug on the 9 th,10th or 11th day of gestation;2. Continued treatment is appropriate from the 9 th to the 12 th day of gestation;3. The drug may be given for 6～15 days if necessary during whole period of gestation.