Abstract: The effectiveness of activitiy of antioxidant enzymes as evaluation index for salt tolerance were investigated in five trees differing in tolerance to salt stress by determining the malondialdehyde (MDA) content and the activities of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX). The results showed that MDA contents of the five trees increased significantly under salt stress. The increasing scales of MDA contents of Syringa microphylla and Pinus sylvestris var. mongolica were larger than that of Ulmus pumila and Lycium dasystemum. The SOD and CAT could serve as reliable indicators for appraising salt tolerance of woody plants, and SOD and CAT were more effective. With the increase of stress intensity, the SOD activities of U. pumila and L. dasystemum increased, while those of S. microphylla and P. sylvestris var. mongolica decreased obviously. POD and APX were not reliable selction criteria. Increase in POD activity did not seem to be a tolerance component, but a stress symptom.