[Objectives]  Long-term use of pesticides has selected for pesticide resistance in pests and environmental pollution. Currently most studies focus on the effects of chemical pesticides on insect enzymes and there have been relatively little research on the immunotoxicity of plant-derived pesticides to insects. [Methods]  Different concentrations of azadirachtin were injected into Oxya chinensis (Thunberg) and hemocyte morphology and the number of various cell types were observed at different times under an optical microscope after Wright-Giemsa dyeing. An enzyme linked immunosorbent assay (ELISA) was used to detect the activity of SOD, POD, PO, AchE, P450 oxidase and CarE. [Results]  The hemocytes of treatment groups showed signs of contracting, vacuole development, threshing and cell deformation. Compared to the control group, the number of plasma cells at different times after injection first increased then decreased, and the number of granulocytes first decreased then increased. The number of hemocytes dramatically increased. SOD and POD activity of the 60 μg/L and 120 μg/L treatment groups were significantly (P<0.01 and P<0.05, respectively) higher than those of the control group between 6 h and 24 h. PO activity of the 120 μg/L treatment group was also significantly (P<0.01) higher than that of the control group over the same time period and AchE activity in all treatment groups was significantly (P<0.01) higher than that in the control group between 10 h and 24 h. CES activity in the 30 μg/L treatment group was also significantly (P<0.01) higher than that of the control group. Although P450 activity was also higher, it was not significantly different to that in the control. [Conclusion]  Treatment with plant-derived pesticides changed the morphology, and quantity, of hemocytes in O. chinensis. Changes in related enzymes activity in hemocytes could be used to infer the immune response of O. chinensis to azadirachtin, and further explore the immune response mechanisms of this species. These results not only provide a theoretical basis for the prevention and control of O. chinensis, but also general a reference for insect immunotoxicology.