Transmission electron microscopy was used to study the ultrastruc-ture of various stages cells and sperm in spermatogenesis and spermiogenesis of ye-llowfin seabream (Sparus latus) in Xipu Bay (a semi-closed bay), Dongshan Coun-ty, Fujian Province. The morphological and ultrastructure changes of nuclei, mito-chondria, Golgi bodies and somatic cells were described and disccused in detail. Thedevelopment of testis and the relationship between maturity ages and body lengthor body weight were also investigated. The results reveal that the testis of this spe-cies could reach maturity in the bay. The spermatogenesis and spermiogenesis process of She fish underwent six stages: (1) primary spermatogonia, (2)secondary sperma-togonia, (3)primary spermatocytes, (4)secondary spermatocytes, (5) spermatidsand (6) formation of sperm ceils. Matured sperm was composed of head, midpieceand tail, there was a horse-hoof like nucleus and without an acrosome over it. Theconeentration process of chromatin was as follows: fine grains form in primary andsecondary spermatogonia, small masses form in primary and secondary spermatocy-res and uniform materials with high electron density in spermatids and maturedsperms. A small proportion of the male mature at Ⅰ year class, but most of themmature at the Ⅱ year class.