The aim of the present study was to investigate the expression changes of three steroidogenic enzymes in the polycystic ovary syndrome (PCOS). Thirty Sprague-Dawley (SD) rats were randomly divided into normal control (NC) group and PCOS group. PCOS rat model was established by DHEA injection. The serum levels of progesterone, estrogen and testosterone were measured by immunoradioassay or enzyme immunoassay. The cellular distributions of 3β-hydroxy steroid dehydrogenase (3β-HSD), 17β-hydroxy steroid dehydrogenase (17β-HSD) and cytochrome P450 aromatase (P450arom) in ovaries were detected by immunohistochemistry. The expression levels of 3β-HSD, 17β-HSD and P450arom were detected by RT-PCR and Western blot. The results showed that the serum levels of estrogen and testosterone of PCOS group were significantly higher than those of the NC group. There was no significant difference of serum progesterone level between the PCOS and NC groups. Compared with the NC group, the PCOS group showed increased mRNA and protein expressions of both 3β-HSD and 17β-HSD, as well as reduced P450arom mRNA and protein expressions. These results suggest that 3β-HSD and 17β-HSD, but not P450arom, may participate in the ovarian hormonal regulation in the present rat model of PCOS.