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In recent years, environmental endocrine disruptors (EEDs) have received extensive attention because of their hormone-like or anti-hormone effects. Dibutyl phthalate (DBP) is not only one of the most widely-used phthalates but also a member of EEDs with the estrogenic property. Although some studies have revealed the negative effect of DBP on the reproductive system, the underlying mechanisms are still elusive. Here the effect of DBP on P450 aromatase, a rate-limiting enzyme stimulated by FSH in the estradiol synthesis, was investigated in human granulosa cell line KGN. Cultured cells were treated with FSH and various doses of DBP (0.1μM, 1μM, 10μM, 50μM, or 100μM) for 24hr. Then the expression of aromatase was assessed, and the synthesis of estradiol was detected to reflect aromatase activity. As shown by the results, all concentrations of DBP could up-regulate the mRNA as well as protein levels of aromatase, and 0.1μM DBP increased the production of estradiol significantly. Furthermore, the ovary-specific promoter of aromatase, promoter II, was activated by 0.1μM DBP, and the expression of FSH receptor (FSHR) was increased by DBP from 0.1μM to 100μM. The study results show that DBP can affect aromatase from both quantitative and functional aspects, and this process may involve the activation of aromatase promoter II and upregulation of FSHR in KGN. Additionally, low-concentration DBP, near human serum concentration, has a more robust effect. This study suggests that DBP may affect the steroidogenic capacity in human ovaries and contributes to our understanding of the effects of DBP on the female reproductive system., (© 2019 by the Association of Clinical Scientists, Inc.)