AIM: To evaluate the long-term effects of gonadotropin-releasing hormone (GnRH)-based vaccine on levels of GnRH antibody and testosterone, and vaccine-induced immunocastration on sexual behavior of male rats.METHODS: The rats were treated with GnRH-PE40 intraperitoneally every other day for 12 wk. GnRH antibody and testosterone level in rat blood were determined by ELISA and radioimmunoassay, respectively. Morphological changes in testes and sexual behavior of rats were evaluated.RESULTS: GnRH-PE40 induced a high production in GnRH antibody, decreased the serum testosterone level, testis atrophy and sexual function in rats.CONCLUSION: Intraperitoneal administration of GnRH-PE40 produces structural and functional castration of male rat reproductive system by inducing anti-GnRH antibody.