This experiment was carried out to investigate the recovery period of estrus cycle, the pseudopregnancy period, weights of ovary, placenta and fetus, and number of litter of female rats after unilateral ovariectomy(ULO). The results obtained are as follows : 1. The estrus cycle was inclined to become normal from the second time. 2. The pseudopregnancy period of rats in unilaterally ovariectomized group and control group, and no significant difference in pseudopregnancy period was shown between the two groups. 3. The ovarian weights of each ULO group were significantly(P<0.01) heavier than that of the control group throughout the observation periods of pregnancy. 4. The placental weights of ULO group were not different from that of the control group in 10 and 15 days of pregnancy. But they became significantly (P<0.05) heavier in 20 days. 5. The weights of fetus in ULO at 10 days of pregnancy was not different from that ofthe control group, but the weights in ULO group at 15 and 20 days of pregnancy were significantly(P<0.01) heavier. 6. The number of litter in ULO was smaller than that of the control groups.