Abstract: The mechanism of inhibitory gonadal precocity of GnRH-A and Zipi in cultured large yellow croaker was studied using pituitary histophysiological methods. The present result s indicate that it occurred vacuole in the cytoplasms of many gonadotropic cells in the pituitary of gonadal precocity, which shows that the cause of gonadal precocity may be due to entering the secretory activity of GtH cells in pituitary. The GtH cells of the cultured large yellow croaker, which had been fed with food containing GnRH-A, showed a weak immunopositive reaction to GnRH ant-i idiotypic antibodies, while those of the gonadal precocity in the control group showed a strong immunopositive reaction. These results indicate that responsive capability of GtH cells in the experimental group to GnRH-A are weakened, and desensitizat ion effect occurred. It may relate with GnRH-A inhibitory gonadal precocity of large yellow croaker. GnRH receptor on the membrane of GtH cell of the cultured fish, which had been fed with food containing Ziqi, did not showed desensitization phenomenon, which indicates the mechanism of inhibitory gonadal precocity of Ziqi differs from GnRH analogues.However, the definitive mechanism still needs further study.