Unanticipated increase in risk for breast cancer and cardiovascular disorders among menopausal women taking hormone replacement therapy (HRT) has been reported (Rossouw et al, 2002). Plant extracts with estrogenic properties are of increasing interest as potential alternatives to using HRT (Wylie-Rosett, 2005). One such alternative includes the phytoestrogens, which are plant substances producing estrogenic effects (Lotke, 1998). Winged bean (Psophocarpus tetragonolobus L.) is a tropical legume grown in Southeast Asia. The chemical composition of its seeds is very similar to that of soybean, a natural source of phytoestrogens (Benito et al, 1982). However, its estrogenic activities have never been investigated. The aim of the study was to examine estrogenic activities of winged bean seed oil (WBSO) in ovariectomized rats (OVX). WBSO was obtained by cold pressed. The animal cares followed the guidelines of the Committee on Care and Use of Laboratory Animal Resources, National Research Council of Thailand and the experiment procedure was performed with the advice of the Institutional Animal Care and Use Committee. 20 Adult female virgin rats (200-250 g) were subjected to operation. 14 days after operation, the rats were divided into 4 groups (n=5); sham operated rats (SHAM) received 1% tween 80 (1 ml), OVX received 1% tween 80 (1 ml; control), OVX received estrogen (0.02 mg/kg BW 17β-estradiol), and OVX received WBSO (1 ml/100 g BW) orally/day for 6 weeks. Vaginal cornification was determined throughout the experimental period. At the end of the treatment the animals were sacrificed. The uterus was removed and weighed. Serum estradiol was also evaluated. The statistical analysis of differences between groups was performed using one way ANOVA. The results showed that WBSO induced an opening of vagina on day 8 and cornification of vaginal epithelial cells which occurred 7 days earlier as compared to control. This was observed in all treated animals (100%). The mean relative uterine weight (RU) was significantly different among groups (P<0.05). RU (%) in SHAM, control group, estrogen-treated group, and WBSO was 0.18±0.00, 0.06±0.01, 0.13±0.01, and 0.09±0.01, respectively. Thus, WBSO significantly increased RU when compared to control, but the increase was lesser than those of estrogen. Serum estradiol (pg/ml) in SHAM, control group, estrogen-treated group, and WBSO was 39.29±1.8, 13.78±1.6, 81.93±18.2, and 52.57±3.6, respectively. Thus, there was a significant increase in serum estradiol with estrogen-treated group and WBSO as compared to control (P<0.05). Taken together, WBSO has estrogenic activities as it can induce vaginal cornification, increase relative uterine weight and raise serum estradiol. WBSO may therefore offer the same uses as soybean.