Abstract: Objective: To investigate the toxic effect of mono-（2-ethylhexyl） phthalate（MEHP） on steroidogenesis in human granulosa cells（GCs）. Methods：Follicular fluid were collected from six patients undergoing in vitro fertilization. GCs were extracted and cultured in vitro for 72 hours, and then treated with MEHP （25，300，500 μmol/L）. After treatment for 48 hours，the expression levels of CYP11A1，PPAR-γ，CYP19A1 and 3β-HSD mRNAs were determined by real-time PCR. Results：The expression of CYP19A1 mRNA in GCs was significantly down-regulated by MEHP treatment of 300 μmol/L and 500 μmol/L（P＜0．05）, and the expression of CYP11A1 was significantly down-regulated by MEHP treatment of 500 μmol/L（P＜0．05）. Also, the expression of 3β-HSD mRNA was decreased by 500 μmol/L MEHP treatment（P＜0．05）, while PPAR-γ expression was increased by 300 μmol/L and 500 μmol/L MEHP treatment（P＜0.05）． Conclusions：MEHP at higher doses affects steroidogenesis in GCs by down-regulating the expressions of steroid biosynthesis enzymes CYP19A1，CYP11A1 and 3β-HSD, and by up-regulating the expression of PPAR-γ.

Key words: Phthalic acids, Germ cells, Estrogens, Progestins