Abstract: The contents of endogenous hormones including gibberellin (GA), indoleacetic acid (IAA), methyl jasmonate (MeJA), abscisic acid (ABA), ribosylzeatin (ZR), brassnioldie (BR) during bolting caused by high temperature in lettuce were determined by ELISA method to discuss their relation with bolting of lettuce. The results showed that GA content in stem and leaves of lettuce during bolting (after 7 days under the high temperature treatment) were significantly higher than before bolting (first 5 days under the high temperature treatment) under high temperature treatment. Compared with the control, GA content in stem were higher. In high temperature treatment, the contents of IAA, ABA, ZR during bolting were higher than before bolting. IAA and ABA were higher in high temperature treatment than the control, while the content of ZR in leaves was different. The content of BR was lower during bolting. Compared with the control, it showed no difference in leaves and significantly lower in stem. The concentration of MeJA in the high temperature treatment group was higher than in the control group and it’s significantly lower during bolting than before. These results indicated that high temperature could promote the bolting of lettuce, which might be connected with high level of endogenous GA, IAA, ABA, ZR and low level of BR, while the concentration of MeJA had no impact on bolting.