This study was conducted to investigate the effects of Cu²⁺ on the weight gain rate (WGR), gonadosamatic index (GI), antioxidant enzyme activities and transcription of major yolk protein gene (MYP) in Strongylocentrotus intermedius. All experimental sea urchins were randomly divided into six tanks (200 L), and each tank was stocked with 20 individuals. Then, the test group was added CuSO₄·5H₂O to a final concentration of 0.02 mg/L Cu²⁺ with natural sea water as the control group. The experiment lasted for 60 days. Results showed that WGR and GI were significantly lower in the test group than those in the control group at 60 days. The activities of CAT and GST in the coelomic fluid of sea urchins in the test group were significantly lower at day 60 than those at day 30, and the activity of CAT was lower in the test group than that in the control group. The MYP transcription was significantly lower in the gonads of the test group than that in the control group, but the expression of MYP was significantly higher in the digestive tract of the test group than that in the control group. The total protein content was significantly higher in the coelomocytes of the test group than that in the control group. Results above showed that the WGR, GI and antioxidant enzyme activities of sea urchins could be reduced by Cu²⁺. This may be caused by inhibiting MYP expression in the gonad and the MYP transportation from the digestive tract to the gonad.