Aim: The early life stress has significant long-term effects on the development of the offspring. This study was undertaken to verify if maternal separation as a stressor agent affects the oxidative status and developmental competence of mouse pre-antral follicles (PF) during in vitro culture period. Methods: Female litters of National Medical Research Institute mice were divided into two groups: maternally separated group (MS), separated from the mothers for 6 h per day from postnatal days 2-16; and the rest considered as the control group, which left undisturbed over the 14 days. The litters were sacrificed and the ovarian tissue was harvested to isolate the PF. The PF were in vitro cultured up to 12th day when ovulation was induced. The developmental parameters and oxidative status (i.e., total antioxidant capacity and Malondialdehyde levels, as well as the activities of superoxide dismutase, glutathione peroxidase and catalase) were assessed. Results: The rates of survival, antrum formation, ovulation and oocyte maturation of PF derived from the MS group were significantly lower compared with those of the control group. Furthermore, the Malondialdehyde level of the MS group was significantly higher than that of the control group. By contrast, the total antioxidant capacity level was lower in the MS group with respect to the control group. Also, the activity of superoxide dismutase, glutathione peroxidase and catalase of PF, derived from the MS group, was significantly lower compared with those of the control group. Conclusion: Early life stress damages the developmental competence of mouse PF through induction of oxidative stress.The developmental competence of PF was assessed by measuring the follicle diameter on the 2nd and 4th day of the cultivation period, antrum formation, 1507