Abstract: Anti-implantation effect of Anordrin in rabbits: A single dose of Anordrin (10.5 mg/kg) was orally administered on day 1 post coitum. Laparotomy was performed on day 11 to examine the number of corpus luteum and implantation sites. The number of implantation sites in the control group was 9.7±1.6, but that in the treated group was 0.3±0.3 (X±SE) Effect of Anordrin on termination of early pregnancy in rabbits: Rabbits were fed consecutively 3 doses of Anordrin (5 mg/kg/d) on days 7,8 and 9 post coitum. On day 17 post coitum laparotomy was performed to examine the development of embryos, the number of normal and absorbed fetuses was recorded. The number of fetuses in the control group was 9.8±1.1, but that in the treated group was 0.2±0.2, dead fetuses 7.4±0.5 Plasma changes of progesterone is relevant to the termination of early pregnancy and pseudopregnancy in rabbits treated with Anordrin. The plasma concentration of progesterone levels started to decrease on the eleventh day after mating. The plasma concentration of progesterone levels was found to fall precipitously on day 9 after treatment with 100 IU of hCG.