Abstract： Objective To investigate the effect of nonylphenol (NP) exposure on the genital development of fetal male rats in pregnant rats,and to measure the mRNA and protein expression of insulin-like factor 3 (Insl-3) in the testicular tissue of fetal rats.Methods A total of 100 pregnant SD rats were equally assigned to blank control group and four NP treated groups.Each rat in the NP treated groups received intragastric administration of NP at doses of 5,40,100,or 200 mg/kg/d from day 14 to 19 of gestation,and the rats in the blank control group received intragastric administration of pure peanut oil.The pregnant rats were sacrificed on day 19 of gestation.The body weight and testicular weight of each fetal rat were measured,and the descent of testis was also observed.The mRNA and protein expression of Insl-3 in the testicular tissue of fetal rats was analyzed by reverse transcription-PCR and Western blot.Results Compared with the blank control group,the 40,100,and 200 mg/kg NP treated groups showed significantly decreased body weight and weight coefficient of testis (P＜0.05 or P＜0.01),significantly decreased testicular descent (P＜0.05),and significantly decreased mRNA and protein expression of Insl-3 (P＜0.05 or P＜0.01).Conclusion Exposure to nonylphenol can lead to testicular maldevelopment,incomplete testicular descent,and Insl-3 expression downregulation of fetal male rats in pregnant rats.