Abstract: In order to explain the reason of resistance to disease in deformed tobacco induced by the residual herbicide quinclorac, the protective enzymes were assayed in tobaccos treated with the herbicide. The results showed that the two enzymes of superoxide dismutase (SOD) and peroxidase POD were activated by quinclorac when planting tobacco on the soil treated with varieties dosage of quinclorac (1.04×10^-3, 2.08×10^-3, 4.17×10^-3, 8.33×10^-3, 1.67×10^-2 mg/kg). The activity of SOD had an increasing trend after treating 14 d, the activity of SOD increased to 9.21%, 32.60%, 109.36%, 136.16%, 151.94% respectively in comparing with the control, But at after 21d, there are no difference among the testing enzyme. The activity of POD in tobacco treated with quinclorac was obviously higher than that of the control and the activity increased continually with the increasing of quinclorac concentration in 35 days. The activity of POD increased to 69.47%, 35.80%, 73.61%, 134.69% and 230.45% in comparing with the control, respectively. The assay of iso-enzymes of POD showed there were more enzyme bands in deformed root treated with quinclorac than that of the control, and the color of enzyme band of the deformed leaf was stronger than the control.