Abstract: Scanning and transmission electron microscopy was used to study the ultrastructure of testis as well as spermatogenesis and spermiogenesis in goldfish, Carassius auratus. The results have shown that goldfish testis consists of somatic cells and germinal cells. The testis has lobular type of organization. The somatic cells in the testis are: myoid cells and fibroblast cells which constitute membrane sheath; cells constituting the interstitium including Leydig cells located between the lobules and Sertoli cells surrounding the cysts. The germinal cells are: spermatogonia, spermatocytes, spermatids and spermatozoa. The cyst cells develop in situ during spermatogenesis. The following features were observed during spermatogenesis and spermiogenesis: 1) Golgi complexes exist at each differentiation stage; their derivates may be important sources of sperm vesicles. 2). Nuclear pores undergo striking rearrangement at different stages. 3) Spermiogenesis can be divided into 3 stages.