Abstract: The effect of gossypol acetic acid on hCG-stimulated progesterone synthesis and secretion in isolated rat luteal cells and its possible mechanism were investigated. When gossypol was used at a concentration of 20μg/ml for one hour, the hCG- stimulated progesterone production and secretion decreased markedly, but the basal progesterone level did not change significantly. The cell viability did not decrease after four hours incubation. The inhibition persisted even when cells exposed to gossypol were washed thoroughly with Eagle solution. Gossypol also reduced the cAMP level. The present experiment indicates that gossypol acetic acid can inhibit the progesterone production stimulated by hCG in isolated rat luteal cells through direct cellular mechanism.