The study was conducted to find out the changes of progesterone and 20$alpha$-dihydroprogesterone (20$alpha$-OHP) levels during the oestrous cycle in Korean native goats. 4 cyclic goats were offered for this experiment. Blood samples were taken from jugular vein on day 0, 1, 3, 5, 7, 9, 11, 13, 15, 17 and 19 during the oestrous cycle, then the next oestrous day. The serum levels of progesterone and 20$alpha$-OHP were measured by radioimmunoassay. The progesterone concentration in seurm of the cyclic goats was 0.29$pm$0.06ng/ml on the first day of oestrous (day 0), increased to 5.29$pm$0.73ng/ml on day 9, reached to a peak level of 5.73$pm$0.61ng/ml on day 13, and thereafter decreased to 0.35$pm$0.30ng/ml on day 1. The serum level of 20$alpha$-OHP during the oestrous cycle was 0.42$pm$0.33ng/ml on day 0 and then decreased to 0.28$pm$0.01ng/ml on day 5. This basal level was maintained until day 13, increased gradually, and reached a peak level of 0.62$pm$0.05ng/ml on day 19. From the above results, it was suggested that the enzyme 20$alpha$-hydroxysteroid dehydrogenase(20$alpha$-HSD) catalyzing the conversion of progesterone to a biologically inactive steroid, 20$alpha$-OHP, should be active in the luteal cells during the oestrous cycle in Korean native goats.