Abstract: Physiological changes of heat tolerance at 36℃ of Lilium formolongi genotype K1-4 and M2-9 were measured during peduncle growth. The results showed that chlorophyll content and protein of genotype K1-4, which was the better heat tolerant growth in field decreased slowly, whereas free proline accumulated rapidly and catalase (CAT) activity was higher. The results indicated that proline was negatively associated to heat tolerance and the three other indexes positively. Heat tolerance of upper young leaves was better than under mature leaves.