Abstract: To study the endocrine-disrupting effects of exposure to mono (2-ethylhexyl) phthalate (MEHP) on marine medaka (Oryzias melastigma) embryos, the medaka embryos were continuously exposed to MEHP (0.01, 0.1, and 1 mg/L) until 10 dpf (days post fertilization), the effects of MEHP on estrogen receptor (ER), peroxisome proliferator-activated receptor (PPAR) and the CYP19 genes at 10 dpf was investigated by real time quantitative RT-PCR method.Results showed MEHP appeared to have no significant effects on the mortality, hatching rates and hatching time of medaka embryos.Treatment with MEHP elicited a significant induction of transcriptional responses of estrogen receptor (ERα) and PPAR receptor (PPARα and PPARγ), 0.01 and 1 mg/L MEHP significantly induced the expression of estrogen receptor (ERγ).MEHP exposure significantly increased the mRNA expression levels of vitellogenin (VTG1, VTG2), Choriogenin (ChgH, ChgL), cytochrome P450 19/aromatase (CYP19a and CYP19b).Meanwhile, MEHP exposure had no significant effect on the expression level of gene androgen receptor α (ARα), which encodes the androgen receptor of marine medaka.Therefore, MEHP exposure can increase the production of estrogen by upregulating the expression of CYP19, leading to diffusion of the estrogen into the target tissue and/or cell and binding to ERs, resulting in the upregulation of ERs (ERα and ERγ), which facilitates their activation, dimerization and binding to estrogen responsive elements (EREs) located in most estrogen-responsive genes such as VTG and Chg, which causing the synthesis of VTG and Chg, resulting in endocrine disrupting effects.