Crofton weed is an Invasive weed in southwestern China.The activities of several antioxidative enzymes involved in plant protection against oxidative stress were assayed to determine physiological aspects of the crofton weed that might render the plant vulnerable to environmental stress.Stresses imposed on crofton weed were heat (progressively increasing temperatures:25℃,30℃,35℃.38℃ and 42℃ at 24 h intervals),cold(progressively decreasing temperatures:25℃,20℃,15℃,10℃ and 5℃ at 24h intervals),and drought(without watering up to 4 days).The three stresses induced oxidative damage as evidenced by an increase in lipid peroxidation.The effect varied with the stress imposed and the length of exposure.The activity of superoxide dismutase(SOD)increased in response to all stresses but was not significantly different from the controls(P＜0.05) when exposed to cold stress.Catalase (CAT)activity decreased in response to heat and drought stress but increased when exposed to cold conditions.Guaiacol peroxidase(POD) and glutathione reductase (GR)activities increased in response to cold and drought but decreased in response to heat stress.The activity of ascorbate peroxidase(APX) responded differently to all three stresses.Monodehydroascorbate reductase (MDHAR)activity decreased in response to heat and drought,and slightly increased in response to the cold stress but was not significantly different from the controls (P＜0.05).The activity of dehydroascorbate reductase(DHAR)increased in response to all three stresses.Taken together,the co-ordinate increase of the oxygen-detoxifying enzymes might be more effective to protect crofton weed from the accumulation of oxygen radicals at low temperatures rather than at high temperatures.