Abstract: ObjectiveRelation between physiological change and chilling tolerance of bitter gourd at seedling stage under cold temperature was analyzed, the suitable sampling time for chilling tolerance evaluation was selected in order to providing references for the accuracy and reliability of evaluating chilling tolerance. MethodBitter gourd materials MC108, MC45 and MC6 seedlings, whose chilling tolerances were various, were stressed at 10 ℃. The physiological in-dexes were measured on leaves at 0,2,4,6,8 and 10 d under low temperature stress. The changes of physiological indexes of materials were drew. Combining the chilling tolerance evaluation results of subordinate function values at different stress times, the suitable sampling time for bitter gourd chilling tolerance evaluation at seedling stage was selected. ResultThe response mechanisms varied in bitter gourd with different chilling tolerances under low temperature stress. Compared with 0 d under low temperature stress(control), soluble protein content decrease of cold sensitive material MC6 at 10 d of stress was larger, proline(Pro) content increase of MC6 was larger. Compared with MC45 and MC6, the change range of superoxide dismutase(SOD) and peroxidase(POD) activities in cold tolerant material MC108 at 2,4,6,8 and 10 d un-der chilling stress was smaller. Apart from malondialdehyde(MDA) content peak, the times of Pro content, soluble protein content, SOD activity and POD activity decrease of MC108, MC45 and MC6 were day 10 under low temperature stress. Combining the chilling tolerance evaluation results of subordinative function values, leaf physiological indexes on day 10 under low temperature stress was the suitable for chilling tolerance evaluation at seedling stage. ConclusionBitter gourd seedlings under 10 ℃ low temperature stress for 10 d is the suitable sampling time for chilling tolerance evaluation.