Abstract: Fish species are being threaten by the high concentration of genistein in water bodies. It is urgent to explore the estrogenic effects and the mechanisms of genistein for aquaculture development and fishery resources protection. Mature individuals of male zebrafish were exposed to a range of concentrations of genistein (1,0, 100,0 μg/L) for 28 days. The study was performed using real-time PCR as a readout to quantify the change in vitellogenin (Vtg-1) mRNA levels. ERα and ERβ1 mRNA levels were then quantified by real-time PCR to explore the action mechanism of genistein. Meanwhile, radioimmunoassay was used to detect the change of E₂ (17β-estradiol) and testosterone levels in gonad of male individuals. The results showed that exposures to 10-1000 μg/L genistein led to dose-dependent increase in Vtg-1 mRNA. The transcriptions of ERβ1 mRNA were significantly stimulated, while the transcriptions of ERα mRNA were significantly inhibited when exposed to 1-1000 μg/L genistein. In addition, genistein treatments enhanced the levels of E₂ and reduced the testosterone levels. The results suggest that genistein may enhance the synthesis of Vtg through increasing endogenous E₂ and ERβ1 levels and thus improve the mediation of ERβ1 for endogenous E₂.