The male genital system of the water mite, Unionicola aegyptiaca consists of an accessory gland, two spherical testes, two vasa deferentia, common vas deferens, an ejaculatory complex and spermatopositor (penis) and is supported with the male genital skeleton. It is evident that each testis is enclosed in a very thin amorphous layer (basal lamina) and consists of a germinal part, in which spermatogenesis take place for sperms development, and a glandular part which consists of a massive complex of glandular cells. The glandular cells of the accessory gland and glandular part of each testis secret testicular secretions which delivered into the lumen of the testis and contribute to sperm cell aggregation and sperm movement. The sperm development of Unionicola aegyptiaca includes spermatogonia, primary and secondary spermatocytes, spermatids and sperms. Fine structures of these stages show mitochondria, rough endoplasmic reticulum, free ribosomes and cytoplasmic vacuoles in their cytoplasm. Transmission electron micrographs show that the mature sperm consists of three parts; head, middle piece and a short tail.