Dynamic changes in content of chlorophll and proline,and activity of protective enzymes such as superoxide (SOD),peroxidase (POD) and chloramphenicol acetyltransferase (CAT) in the leaves of Trapa bispinosa treated,respectively,with Cd²⁺ at varying rates and Cd²⁺ plus 5 mg L^-1 Ce³⁺ were studied.Results show that chlorophyll contents decreased with increasing Cd²⁺ concentration,while the activity of both SOD and POD,and the content of proline increased when Cd²⁺ concentration was low and decreased when it was high.In contrast,CAT activity decreased when it was low and increased when it was high.Compared with the single ion treatments,the Cd²⁺+Ce³⁺ treatments increased cholorophyll contents,and stimulated activity of SOD and POD,especially,that of the latter,which was 8.33 times higher than its control when the combination was 5 mg L^-1 Ce³⁺ plus 1 mg L^-1 Cd²⁺.The results suggest that the addition of 5 mg L^-1 Ce³⁺ can relieve the toxicity of a low concentration Cd²⁺ on leaves of Trapa bispinosa.