In order to study the mechanism of follicular atresia, follicles were classified into the normal groups and the atretic ones, according to the criteria with or without corpus luteum, size of follicles, vascularization, status of granulose cells and the hypertrophy of theca layers in the porcine ovary. To estimate the binding capacity of human chorionic gonadotropin (hCG) receptor on the granulosa cells during atresia, hCG were iodinated by the chloramine-T method and then purified through the column chromatography. The concentration" of hCG receptor in each group were measured by the hCG receptor binding assay. Binding capacity in large normal follicles were 1.16%, but atretic ones were 0.45%. But in medium and small follicles (below 6mm in diameter), the binding capacity in normal follicles were 0.09%, but atretic ones were 0.05%, which was lower than those of large follicles. The present ( ) that the concentrations of hCG receptors on granulosa cells is decreased when the follicles become atretic and be used as a sort of creteria for the identification of follicles atresia.