Abstract: AIM:To observe the luteolytic effects of DL111-IT in pseudopregnant rats. METHODS:Radioimmunoassay was used to estimate serum progesterone concentration and PGF_2α content in uterus and serum; the activities of 3β-HSD and 20α-HSD in ovaries were assayed spectrophotometrically. RESULTS:DL111-IT was shown to shorten normal pseudopregnant period of rats by 4.8 days and decrease ovarian fresh weight, protein content and serum progesterone level dramatically. After im DL111-IT for 5 d, activities of 3β-HSD of pseudopregnant rats decreased 53.8%, while that of 20α-HSD incresed significantly after only one injection of DL111-IT (control: 1.0±0.4 mu.mg^-1 protein; treatment: 6.9±1.8 mu.mg^-1 protein); PGF_2α concentration in uterus and serum of pseudopregnant rats increased 40.1% and 36.5%, respectively. CONCLUSION:DL111-IT induced luteolysis in pseudopregnant rats.