Abstract: The effect of N+ ion implantation on the antioxidative system (SOD、CAT)and MDA content of liquorice seedlings(Glycyrrhiza uralensis Fisch )under PEG-induced drought stress was investigated in this study. The results showed survival ratio of liquorice seeds exhibited saddle-shaped curve. When the dose was 4.1×1016 N+/cm2, the survival ratio was the lowest, while the survival ratio was higher than that of control when the dose increased to 4.6×1016 N+/cm2. MDA measurement pointed out that the contents were significantly lower in seedlings irradiated by N+ ion beams of 4.6×1016 N+/cm2 dose when compared to control. The data also showed that SOD and CAT activity of irradiated seedlings by dose of 4.6×1016 N+/cm2 ion beam were higher than control, indicating that this implantation was useful in enhancement of drought resistance of liquorice seedlings. Result of SOD isoform pattern also demonstrates the biological effects of N+ ion implantation.