Abstract: Spinibarbus caldwelli (Nichols) belongs to the family Cyprinidae, Barbinae.It is now becoming an important fish for aquaculture in China. The testicular histology and spermatogenesis of the fish have not been reported. In May and June 2001,the testes of 5 male Spinibarbus caldwelli were sampled for histological observation under both light microscope and transmission electron microscope. The testis was lobular type,which was typical of most teleosts. It consisted of seminiferous lobuli, interlobular septum,cavum ampulla and vas efferens.In the outer layer of the testicular cortex,the seminiferous lobuli arranged radially,similar to that of the order Perciformes.However in the inner layer of the cortex,the distribution of the seminiferous lobuli was more irregulary. That was similar to those in most fishes of Cyprinidae. The seminiferous lobulus consisted of various stages of spermatogenic cells and Sertoli cells .The spermatogenic cells consisted of primary spermatogonia, secondary spermatogonia, primary spermatocytes,secondary spermatocytes and spermatids.The primary spermatogonia distributed singly.Besides primary spermatogonia,other stages of spermatogenic cells were in the spermatogenic cysts. The wall of the spermatogenic cysts was made of Sertoli cells. Within a spermatogenic cyst,all the spermatogenic cells were at the same developmental stage.Mature sperms were released from the cysts and trnasfered into the lobular lumen.Whitin the cytoplasm of the Sertoli cells,there were lots of electron dense granules.One of the important functions of the Sertoli cells was to engulf and eliminate degenerated spermatids.According to the morphyology of the granules and spermatogonia's sleeves and flagella existing in the cytoplasm of the Sertoli cells,the granules might be the nuclei of the spermatids, which were engulfed by the Sertoli cells. All the lobular lumen converged at the ventral side of the testis, and formed cavum ampulla,which was at the orientation from anterior end to the posterior end of the testis.The morphology of the cavum ampulla was irregular. There were many ridges on the inner surface of it.Outside the cavum ampulla, there was a vas efferens which ran parallel to the cavum ampulla.The cavum ampulla and the vas efferens communicated with each other.Both cavum ampulla and vas efferens were full of sperms. A seminal vesicle connected with the posterior end of either testis.Within the seminal vesicle there were many irregular cavities which were full of sperms. There were, however, no spermatogenic cells in the seminal vesicle. So the function of the seminal vesicle was to store sperms. It was believed that there was no seminal vesicle in the fish of family Cyprinidae.Although Spinibarbus caldwelli belongs to the family Cyprinidae it possessed seminal vesicle.The vas efferens extended from the testis, and entered into the seminal vesicle. It was oriented at one side of the seminal vesicle. Both seminal vesicles connected with a vas deferens. The epithelium of the vas deferens was secretory. The spermatogenesis,similar to that of other teleosts,included the spermatogonia proliferation, two meiotic divisions of spermatocytes,and the spermiogenesis. Primary spermatogonia were the largest germ cells in the testis. Their nuclei were characterized by uncondensed chromatin.There were many concaves on the surface of the nuclei.In each concave there was a electron dense chromatoid body.The chromatoid bodies also could be seen in the cytoplasm, which were generally associated with mitochondria. Like other teleosts,primary spermatogognia of Spinibarbus caldwelli were stem germ cells in the testis.Each primary spermatogonium proliferated,resulted in the formation of a spermatogenic cyst,in which there were many secondary spermatogonia .The nuclei of the secondary spermatogonia were generally more electron dense than that of the primary spermatogonia.The distribution of the chromatoid bodies in the cytoplasm of the secondary spermatogonia was similar to that in the primary spermatogonia.