The estrogen-like effects of 4-nonylphenol（4-NP）in vivo of female Carassius auratus were investigated in this paper. We gave intraperitoneal injection in female Carassius auratus with the dose of 1 mg·kg-1, 50 mg·kg-1, 100 mg·kg-1 of 4-NP or 1 mg·kg-1 of 17β-estradiol (E2) respectively. The expression of α-type estrogen receptor (ER-α) and CYP1A in liver was evaluated by RT-PCR and the concentration of E2 in serum was measured by fluorescent immunoassay in 24 h and 48 h of injection. The results show that 1 mg·kg-1 of E2 increased expression of ER significantly both in 24 h and 48 h (P<0.01). In 4-NP treatment group, the concentration of E2 was decreased and the expression of ER was increased with the increase of 4-NP’s level. In 1 mg·kg-1 of 4NP treatment group, there is a significant increase of expression of ER at 24 h (P<0.01) and 48 h (P<0.05), the concentration of E2 was decreased at 24 h (P<0.05) yet returned slightly at 48 h, and CYP1A’s expression is up-regulated at 24 h (P<0.05) and 48 h (P<0.01). In 50 mg·kg-1 of 4-NP treatment group, there is a significant increase of expression of ER at 24 h (P<0.01) and 48 h (P<0.05), the concentration of E2 was decreased significantly both at 24 h and 48 h (P<0.01), and CYP1A’s expression is up-regulated at 24 h (P<0.05) and 48 h (P<0.01). In 100 mg·kg-1 of 4-NP treatment group, there is a significant increase of expression of ER both at 24 h and 48 h (P<0.01), the concentration of E2 was decreased significantly at 24 h (P<0.05) and 48 h (P<0.01), and CYP1A’s expression is up-regulated (P<0.01). Effect of increasing of ER’s expression is E2>100 mg·kg-1 4-NP >50 mg·kg-1 4-NP >1 mg·kg-14-NP; effect of decreasing of concentration of E2 is 100 mg·kg-1 4-NP >50 mg·kg-1 4-NP >1 mg·kg-14-NP. The effect of 100 mg·kg-1 of 4-NP on ER’s expression is close to that of 1 mg·kg-1of E2, this indicates that 4-NP has weak estrogen-like effects. And 4-NP can up-regulate the expression of CYP1A (dose dependent). That increase in ER’s expression and decrease in E2 in 4-NP treatment group provide support of 4-NP’s endocrine disruption via ER pathways in Carassius auratus. 30 Refs.In Chinese.