The testis structure,development regularity and spermiogenesis of sexually mature Coilia nasus were studied by using paraffin sections and H.E.staining method.The results indicated that,the male gonad of Coilia nasus was composed of testis (sperm production),seminal vesicle and spermatic duct.The spermary had typical lobular structures,which is composed of seminiferous lobula,follicle,interstitial substance,lobular cavity and efferent duct.The seminiferous lobula was composed of spermatogenic cells of varied stages and supporting cells,and spermatogenic cells of varied stages and supporting cells formed the follicle.The mature sperm was released from the follicle into the lobular cavity,then entered into efferent duct via transient pathway formed between lobes,and then was sent into the seminal receptacle.The seminal receptacle was in reticulated structure,and the inner wall was composed of excreting cells.The sperms develop through 5 stages,including androgone,first spermatocyte,secondary spermatocyte,spermatoblast and mature sperms.Six stages were classified according to the appearance,color,volume and vascular distribution of the spermary.