Ultrastructural observations on the female reproductive organs of the Savi's pipistrelle, Pipistrellus savii velox (spring samples) and Endo's pipistrelle, P. endoi (autumn samples) revealed that both the species belong to the‘prolonged sperm storage’ type which is accompanied with prolonged survival of the Graafian follicle, and that the principal site of sperm storage was the uterotubal junction in P. s. velox and the isthmus in P. endoi. Uterine spermatozoa seemed to be dead judging from their degenerating appearance in the former species, and were disintegrating beyond recognition even soon after copulation in the latter. In this context, a comparison of the uterine environments for spermatozoa among three Pipistrellus species including the Japanese house bat, P. abramus, in which uterine spermatozoa oriented towards epithelial cells are capable of living (Uchida & Mori, 1987), demonstrated that the life or death of uterine spermatozoa would be closely related to the nature and amount of secretory granules in the epithelial cells and the quantity of glycocalyx covering epithelial microvilli. The device to protect against polyspermy in P. s. velox appeared to be the zona block.