Abstract: ObjectiveIn order to provide theory basis for understand cold-resistant mechanism and early breeding of cold-tolerant potato varieties, physiological responses of different potato varieties to cold stress was studied at seedling stage. MethodCold-sensitive varieties viz., Favorita, Zhongshu 3 and cold-tolerant potato varieties viz., Guinongshu 1, Guinongshu 4 were used as tested materials, and treated by cold stress at 5℃in artificial climate box. Activities of perox-idase(POD), catalase(CAT) and superoxide dismutase(SOD) and contents of soluble sugar, soluble protein, malonalde-hyde(MDA) and proline under were determined after 0, 1, 2, 3, 5 and 7 days of cold stress, respectively. ResultRe-sults showed that, leaf damage began to appear on exterior of potato seedling after 3-day prolonged cold stress at 5 ℃, and there was distinctive difference among varieties after 5-day cold stress. In addition, after cold stress, activities of POD, CAT, SOD and contents of soluble sugar, soluble protein and proline in leaves of all varieties increased gradually as a whole, and their peak values for different varieties were different. However, variation trends of all physiological in-dexes in different varieties were different with the increase of cold stress time. After 5-day cold stress, enzyme activities and proline contents of cold-resistant varieties were higher than those of cold-sensitive varieties, contents of soluble sugar and soluble protein in the potato variety Favorato were significantly lower than those in the other varieties(P<0.05, the same below). Furthermore, MDA content in the leaves of all potato varieties increased after cold stress, and MDA content in cold-sensitive varieties was higher than that in cold-resistant varieties after 5-day cold stress. Correlation analysis showed that, SOD activity was significantly positively correlated with soluble sugar content, but significantly negatively correlated to MDA content;POD activity was significantly positively correlated with CAT activity and proline content;CAT activity was extremely significantly positively correlated with proline content (P<0.01). ConclusionActivities of POD, CAT and SOD, and contents of MDA and proline in potato leaves can be used as physiological indexes to identify cold re-sistance, and the optimal time for early screening cold-resistant materials is at the 5th day after cold stress. Cold resis-tances of four potato varieties at seedling stage are ranked as follows:Guinongshu 4>Guinongshu 1>Zhongshu 3>Favorita.