Several species of the genus Pipistrellus (Vespertilionidae) store spermatozoa for prolonged periods prior to ovulation, but the reproductive strategy used by Pipistrellus kuhlii remains unknown. In order to investigate the prevalence of sperm storage in the bats of this genus we documented endometrial sperm storage in the uterus of two female Pipistrellus kuhlii collected during mid-December in western Iran. The uteri were distended with densely packed spermatozoa, those at the periphery exhibiting perpendicular orientation toward the endometrum. This orientation, together with the fact that copulation is unlikely to occur at this time is used to infer that P. kuhlii stores sperm over the winter.