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OBJECTIVES: Estrogen plays an important role in for growth and development of reproductive system in female. The major royal jelly (RJ) has a significant estrogenic-like effect for many female animals. The major RJ proteins (MRJPs) are the central constituents responsible for the physiological activities of RJ. In recent years, we have found that MRJPs possesses functions to increase fecundity associated with estrogenic effect in Drosophila. However, if MRJPs are the specific active ingredient mediating estrogenic effect of RJ and related action mechanism in mammalians remains unclear. METHODS: Neonatal immature female mice (FC) were divided into four groups fed MRJPs with doses of 0, 125, 250 and 500 mg/kg/body weight (M125, M250 and M500), respectively. The freeze-dried MRJPs powder was administrated daily for 45 consecutive days. The effects of MRJPs on the puberty onset, ovarian follicular development and serum estradiol levels in FC were evaluated. RESULTS: The times of estrus in M125, M250 and M500 were accelerated by 10.7%, 15.5% and 10.7%, the ovarian index of M125 and M250 and M500 were increased by 26.8% and 32.1% and 1.7%. The number of secondary follicles in M125 and M250 and M500 were increased by 50.7%,78.8% and 38.6%, the Graafian follicles in M125 and M250 and M500 were increased by 600.0% and 774.0% and 150.0%. M500 induced multi-oocyte follicles. The serum estradiol levels of M125, M250 and M500 were increased by 47.1%, 64.9% and 31.1%, the action of MRJPs raising hormone secretion level is mainly via upregulating expression of ERβ gene. Antioxidant parameters of ovarian tissue showed that the malondialdehyde levels in M125 and M250 were decreased, the superoxide dismutase activities and glutathione peroxidase activities in M125 and M250 were increased, respectively. CONCLUSIONS: Oral administration of MRJPs may accelerate onset of puberty and promote follicular development in immature FM. The reproductive performance promotion of MRJPs was associated with raising estrogenic activity and antioxidant potential to reproductive system, upregulating expression of ERβ gene to raise hormone secretion and promote ovary development in FM. FUNDING SOURCES: The National Natural Science Foundation of China and US Department of Agriculture, Agriculture Research Service.