Changes of chlorophyll content, soluble protein content, O₂· generating rate and activity of protective enzymes (SOD, POD, CAT) in leaves of Potamogeton crispus Linn, under different concentration gradient of Cd²⁺ stress or exogenous acetosalicylic acid treatment were studied and analyzed.The results showed that exogenous acetosalicylic acid could increase chlorophyll and soluble protein content clearly, and markly enhance activity of protective enzymes.At the same time O₂· generating rate was lower than those of trearaent under single Cd²⁺ stress.So it was concluded that acetosalicylic acid could alleviate the toxic effects caused by Cd²⁺ stress.