Abstract: Eighteen potato cultivars and forty-seven strains were tested for their abilites to tolerate frost and freezing temperatures. Leaves freshly detached from the potato plants were exposed to low temperatures for electric conductivity measurement to derive the medium lethal temperatures, LT₅₀, on each sample. As temperature was lowered, the relative electric conductivity of the potato leaves responded in a typical S function in a logistic equation. The LT₅₀ obtained from the regression equation varied from -3.8℃ to -1℃. They significantly differed among different cultivars and stains. Based on LT₅₀, cold resistances of the various potato cultivars and strains were predicted and clustered into 3 categories, sensitive, medium, and tolerant to freezing. Among them, the two cultivars and 4 strains most tolerant to freezing were preserved for breeding low-temperature resistant varieties in the future.