Our study aimed to compare between the efficiency of kisspeptin-10 (Kp10) and gonadotropin-releasing hormone (GnRH) as a trigger stimulator for gonadotropins; luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone (T) in male calves. Four prepubertal male Japanese Black calves were used. The animals were given GnRH or Kp10 separately. Plasma LH and FSH concentrations were measured by radioimmunoassay (RIA) and T concentrations were assayed by enzyme-linked immunosorbent assay (ELISA). Gonadotropins were significantly increased in response to injections of GnRH and Kp10. However, the response of gonadotropins-release was significantly greater to GnRH than to Kp10 (P<0.05) throughout the 180-min period. Plasma T concentrations increased significantly following injection of Kp10 or GnRH (P<0.05) in comparison with the pre-injection levels (0.75 - 0.47 ng/ml) but no significant difference was observed in T-releasing in response to GnRH and Kp10 throughout the 180-min period. Histopathologically, the testicular tissue had seminiferous cords, essentially without lumina, rather than seminiferous tubules. The basal lamina was very thick and surrounded the immature ill-developed Sertoli as well as spermatogonia cells. Neither spermatid cells nor sperms were seen (no spermatogenesis) with abundant interstitial tissue. No differences in structure of testes in Kp10 or GnRH-injected claves and those of control. Conclusively, GnRH and kisspeptin stimulated equally the secretion of T in prepubertal bulls but did not affect process of spermatogenesis.