Abstract: Objective Nonylphenol is used widely as plastic additives and surfactants.Recent reports demonstrated alkylphenols are estrogenic.However,the effect of them on animal development remiains unknown.This study is designed to investigate the possible effects of nonylphenol on early development in SD rats.Methods Thirty four pregnant rats are exposured to p-nonylphenol at 0.1%,0.5%,1.0% levels during last ten days of pregnancy.Birth weight,uterus weight of F1 are measured,and morphological characters of uterus and ovary and expression of PCNA and ER are analyzed by histochemistry and immunohistochemistry.Results Nonylphenol at all levels decreased birth weight(P<0.01)and increased uterus weight (P<0.01).Three groups of nonylphenol had more primary and second follicle than the control(P<0.01).The expression of PCNA in granule cell of follicle was enhanced(P<0.05)in 0.1% and 1.0% p-nonylphenol.Conclusion p-nonylphenol can promote early ovary follicle development and increase uterus weight.