Abstract Monocrotophos (MCP) is listed as a Prior Informed Consent chemical, and it is still used extensively in developing countries. It has been seen that MCP shows high toxicity in fish and aquatic ecosystems. To confirm whether MCP shows estrogenic effects on fish, the induction of vitellogenin (VTG) in male goldfish ( Carassius auratus) following a 21 day exposure to 0.01, 0.10 and 1.00 mg·L − 1 40% MCP pesticide in a semi-static exposure system was evaluated by hepatic mRNA and plasma protein. Real-time reverse transcriptase polymerase chain reaction assay showed that MCP significantly increased hepatic mRNA expression of VTG in male goldfish in a dose-dependent manner. Western blot analysis revealed the presence of two VTG subunits with molecular masses of 134 kDa and 110 kDa in the plasma of the exposure groups, which were not observed in that of the control males, indicating the induction of VTG protein synthesis and secretion by MCP in male goldfish. Furthermore, the levels of plasma VTG protein in the control group and the 0.01, 0.10 and 1.00 mg·L − 1 40% MCP pesticide exposure groups were quantified by enzyme-linked immunoassay, and revealed concentrations of 53.8 ± 5.6 ng·mL − 1 , 285.5 ± 5.0 ng·mL − 1 , 972.9 ± 7.4 ng·mL − 1 and 678.4 ± 38.0 ng·mL − 1 , respectively. The overlapping results of VTG mRNA and protein indicated that MCP had significant estrogenic properties and was thus a potential endocrine disruptor.