Empirical growth curves were derived by measuring length of forearms, body mass and length of the total gap of the fourth metacarpal-phalangeal joint in a free ranging population of the Mehely's horseshoe bat (Rhinolophus mehelyi) in a maternity roost in western Iran. Length of forearm and body mass followed a linear pattern of growth until day 14 and subsequently decreased to reach a stable level. The length of the gap of the metacarpal-phalangeal joint showed an increase up to 10 days and decreased until it had closed at over 55 days. Initiation of flight occurred approximately four weeks after birth. During the first two weeks of postnatal growth, the body mass and the length of forearm of pups increased linearly at mean rates of 0.58 g/day and 1.55 mm/day, respectively. A method of estimation of age was derived from values of forearm length and the total gap of the four metacarpal-phalangeal joint during the preflight and post flight periods.