Immunohistochemical localization of LHR and AR was performed by using rabbit antiserums against leuteinizing hormone receptor (LHR or choriogonadotropin receptor CGR) and androgen receptor (AR). The aim of present study was to reveal the endocrine mechanism of exogenous gonadotropin (CPH and hCG) inducing spermatogenesis in testis of Japanese eel. The results showed that the testis and spermatogenesis in Japanese eel displayed very marked changes after hormone injection. The observation of histological section showed the testis of eel was at the stage of spermatogonia proliferation before hormone treatment, while ten days after the injection of the combination of two gonadotropins, the spermatogonia mitosis and number increase of primary and second spermatocytes in the lobule of testis of male eel were seen. Thirtyfive days after hormone treatment, a lot of primary and second spermatocytes in the lobule of testis as well as some sperms in the lumen of seminiferous tubule, except a few spermatogonia near reproductive epithelium, could be seen. Eightthree days after hormone treatment, the spermatogenesis and the development and maturity as well as spermiation of testis in male eel completed. Immunohistochemical staining results further revealed that LH or CG receptors immunoreactivity was located on the reproductive epithelium showing strong immunopositive reaction before hormone treatment, while LH receptors immunoreactivity was located on the cytomembrane of Sertoli cells, Leydig cell or interstitial cell, spermatogonia, primary and second spermatocytes showing strong immunopositive reaction after hormone treatment. Before hormone treatment, androgen receptors were located on the cytomembrane of spermatogenic cells and reproductive epithelium, while AR were located within nucleus or in cytoplasm of these spermatogenic cells, but spermatids and sperm showed immunonegative reaction. The results demonstrated for the first time that the action mechanism of two hormones inducing spermatogenesis and maturity in eel is mediated by their corresponding receptors. Thus, the present study will provide scientific basis for the dosage and intervallic time of injecting hormones during artificial propagation of eel.