The effects of low temperature stress on photosynthesis in leaves of seven regular potato cultivars and two Hunan endemic potato species have been studied. The results showed that the photosynthetic rate (Pn) was significantly reduced with decreasing environmental temperature for all the species, however, every species exhibited different declining rate. For example, the maximum net photosynthetic rates(Pnmax) between 10 ℃ and 20 ℃ treatments of Jinshanshu, Zhongzaihuangpi, Zhongshu3, Zhongshu5, Xiangshu1, Favorita were reduced by 51.0%, 33.4%, 44.5%, 42.6%, 14% and 17% respectively, where the Pnmax variations in these two groups of treatments reach significant level(P<0.05). On the other hand, the decreasing rates of Pnmax of Kexin series (1, 3, 4) were within 4.5% , and insignificant variations were found between 10 ℃ and 20 ℃ treatments(P﹥0.05). The apparent quantum yield(AQY), the light saturation points(LSP), the light compensation points(LCP), stomatal conductance(Gs) and transpiration rate (Tr) were significantly decreased under 10 ℃ temperature stress(P<0.05).The Pnmax values of Favorita, Zhongshu3 and Xiangshu1 under 5 ℃ temperature stress were 9.85, 7.54, 5.13 μmol/(m2•s) respectively, while Pn values of the other materials were essentially zero. Increased intercellular CO2 concentration (Ci) were observed after an obvious declination when the environmental temperature decreased from 10 ℃ to 5 ℃. The above results indicate that the photosynthetic rateunder 5 ℃ low temperature stress can be served as a promising index in for evaluation of seedling cold tolerance.