The present work deals with the study of the population ecology of two sympatric species of insectivorous bats in Saqqara area, Giza Governorate, Egypt; the tomb bat, Taphozous  perforatus E. Geoffroy 1818, and the lesser mouse-tailed bat, Rhinopoma  hardwickii Gray 1831.  Field and laboratory work continued for 24 months (January 2012 - December, 2014) and focused on such topics as age estimation, changes in sex-ratio, reproductive cycle, age structure, and seasonal changes in body weight. A total of 331 individuals were collected throughout the study period (211 individuals of T. perforatus and 120 individuals of R. hardwickii). The determination of relative ages of both bat species depends on measuring the lengths of their forearms. The study of sex-ratios indicated that males of both bat species slightly outnumbered females in the total sample collected during the study period. These ratios showed noticeable differences between sub-adults and adults of both bat species. The reproductive strategy of T. perforatus depends on storing sperms by females after copulation in late autumn months followed by delayed pregnancy, delivery and lactation in late winter, spring, and early summer month. Each pregnant female gives birth to only one young. Reproductively active males of T. perforatus were only collected in late autumn months and those of R. hardwickii, were collected in late autumn and winter months. The study of the age structure indicated that adults outnumbered sub-adults in the total populations as well as in both sexes of the two bat species with the exception of female R. hardwickii. The seasonal changes in the age structure were generally related to the reproductive cycle of these two bat species. The low percentage of sub-adults indicated that the population growth rate of bats is low. The body weight of both sexes of both bat species clearly increased with the increase of individual ages. Males had highest mean body weights in autumn months (months of sperm production), while females had highest mean body weights in spring and summer months (months of pregnancy and lactation). The results of the present work are of special interest to wildlife conservationists, agricultural authorities, pest control specialists, public health authorities, and environmentalists.