Study of the impacts of environmental factors on sperm properties of fishes needs understanding its structure. Since. There is no information is available about morphological structure of Caspian lamprey (Caspiomyzon wagneri). Hence, this study was conducted to survey the histo-morphology of testis and structure of the spermazoid in Caspian lamprey during spawning season. For histological examination, the testis of 15 Caspian lampreys were sampled during their migration to the Shirud River and then, the histological section of these samples were prepared based on paraffin method. For study of the morphological parameters of the spermatozoid, including the shape and length of spermatozoid; length, width and area of the head, length and width of the flagellum, ellipticity and elongation of the spermatozoid, they were studied by Scanning Electron Microscopy (SEM) immediately after spermation and fixation in glutaraldehyde fixative solution. The results showed that the Caspian lamprey has a lobular testis enclosed by interstitial cells, fibroblasts, blood vessels and lymphatic vessels. During the sampling time (mid-May), fish testes were at stage V and full of the spermatozoa. SEM results showed that the sperm of this species compared to other lamprys is shorter and has a smaller head length with less elongation as well as flat anterior face of the acrosome.