Abstract: To investigate the effects of microplastics on biological growth and metabolism in culture environment, Chinese mitten crab (Eriocheir sinensis) was selected to be exposed in different particle sizes(5 and 50 μm) and different concentrations (0.1, 1, and 10 mg·L^-1) of microplastics for 28, 35 and 42-day toxicity test. Survival and weight gain rates were recorded to evaluate the effect of microplastics on the growth of crabs. Superoxide dismutase (SOD)、catalase (CAT) activities, and malondialdehyde (MDA) content in the hepatopancreas of the crabs were measured simultaneously to study the effects of microplastic on antioxidant enzyme activities. The results show that exposure in microplastics did not affect the survival rate of juvenile crabs, but there was a decreasing trend in the weight gain as the exposure concentration increased. The variation of SOD and CAT activities in the hepatopancreas of 5 μm groups was greater than that of 50 μm groups. Small-sized microplastics had a greater influence on the oxidative stress system than big-sized microplastics in E.Sinensis, but without significant regularity. At the same concentration, there was a significant effect in the middle stage of treatment. SOD and CAT activities were most induced in the 35 days of exposure. SOD activities were inhibited to different degrees in the early exposure, while CAT activities showed a trend of increasing first and then decreasing with the exposure time. With prolonged exposure time, the induction effect gradually weakened until the 42nd day. The content of MDA reached the highest level on the 28th day of exposure, then the increasing trend of MDA content gradually decreased. Under the same exposure time, the effect of low concentration of microplastics was significant, while the high concentration of microplastics exposure produced some inhibitory effect. The results indicate that the low concentration of microplastics could cause oxidative stress to E. Sinensis for a short time and affect the activity of the antioxidant system in the hepatopancreas, while high concentration of microplastics for a long time could significantly inhibit the activity of various enzymes in the hepatopancreas, causing damage to the oxidative system in juvenile crabs.