Abstract: Objective To study adverse effects of nonylphenol(NP) on thymus tissue and thymocytes of female Sprague-Dawley(SD) rats,and to investigate the effects of NP on immune function of female SD rats.Methods Thirty-two female SD rats were randomly divided into four groups(8 in each group) and treated with NP through gavage at the doses of 0,20,80,and 200 mg/kg once two days for 60 consecutive days.At the end of the experiment,the pathological examination of the thymus was done and the level of reactive oxygen species(ROS),intracellular free calcium concentration(Ca²⁺_i),and mitochondrial membrane potential(MMP) in thymus lymphocytes were detected with flow cytometry.Results Compared with the control,the rats' thymus weight significantly decreased in 200 mg/kg NP treated group,with a singnificant difference(P<0.05).The thymus weight correlated negatively with exposure concentration(r=-0.317,P<0.05).The levels of ROS in thymus lymphocytes were increased dramatically in 200 mg/kg NP treated group in a dose-dependent manner(r=0.488,P<0.05),with a significant difference(P<0.05).Histopathological changes were found in the thymus of the experimental groups with the thined cortex.Conclusion Exposure to nonylphenol by oral route may induce adverse effects on the thymus and thymus lymphocyte in rats and affect the immune function of female rats.