Abstract: Changes of carbohydrate contents, sucrose-metabolizing enzymes activities and chloroplast ultrastructure in tomato（Lycopersicon esculentum Mill.）leaves that were treated by 30 ℃ and 35 ℃ were studied to investigate the effects of high temperature on carbohydrate metabolism of tomato. Plants were treated by 30 ℃ and 35 ℃ in daytime after the 1st inflorescence effloresced, and plants that under 25 ℃ were considered as control. Results showed that the chloroplast ultrastructure in high temperature treated plants leaves changed and the number of starch grain in chloroplast decreased firstly then increased obviously after plants had been treated for 15 days, especially those plants that were treated by 35 ℃. Fructose content, glucose content and sucrose content in treated leaves all decreased compared to control. The higher the temperature in daytime was, the bigger differences between treatments and control were. The activities of acid invertase (AI) and neutral invertase (NI) in treated leaves decreased, but the activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) increased when plants were treated by high temperature for 15 days. It was maybe the changes of chloroplast ultrastructure，carbohydrate accumulation and metabolism in leaves that made the disadvantage effects on growth and development, yield and quality of tomato. The higher the temperature was, the worse effects they made.

Key words: Tomato, high temperature in daytime, carbohydrate, sucrose-metabolizing enzymes