Abstract: The spermiogenesis of Pagumogonimus skrjabini was observed on the ultrastructural' level by trasmission electron microscopy. The development and the morphological characteristics of spermatids and sperm were studied. The Golgi comples was located near the anterior region of the spermatid nucleus and developed into an acrosomal cap of the sperm. Accordingly, an acrosomal structure of P. skrjabini was recognized in this study.The mature sperm of P.s. was composed of head and tail. The head part was filled with dense nucleus and the nucleoplasma extended into the anterior end of the median part of the sperm tail. A conjunction part was seen between the head and the tail. The tail was composed of a median part and a terminal part. At the beginning of median part of the tail, two axial filaments were found on each side. Each axial filament was composed of two central filaments and nine pairs of outer filaments. The two central filaments were surrounded by fibrous sheath, both of which were connected with spoke-like structures. Mitochondria were arranged in a line in the ventral portion of the central filaments. At. the terminal part of the tail, two axial filaments lay closely together.