Oxytocin (OT) possesses uterotonic and galactopoietic properties. To the best of the knowledge, the relevant data regarding to the estrous cyclicity was scared. The present study investigates the chronic effect of low dose OT on estrous cyclicity in detail by using rodent model albino mice.  Twelve immature female mice, Mus musculus weight 8±2g were divided into 2 groups as control (n=6) and treated (n=6). The treated and control groups were received intraperitoneal (i.p.) dose of synthetic oxytocin (50mIU/5µl/g body weight) and physiological saline (5µl/g body weight) respectively for 90 days from postnatal day 10 (PND 10) to PND 100. Day of vaginal opening and first onset of estrus as well as estrous cycle study were done. The major observations during the research study were that, OT was showed significant decrease day of vaginal opening and first onset of estrus as well as significant shorten the length of estrous cycle as compared to control group. Finally the research study was concluded that, synthetic OT altered sexual maturity as well as estrous cyclicity of mice at selected dose and duration; therefore a care must be taken for long term use.