Abstract: The objective of this study was to investigate leaf tissue characteristics under heat stress in thermo-resistant cultivar and thermosensitive cultivar of Brassica campestris and B.oleracea with the methods of microscope,scanning electron microscope,the results obtained are summarized as follows:1.Leaf abaxial epidermis of thermo-resistant showed higher stomatal density, smallar stomatal openning area than thermo-sensitive cultivar under SEM, some stomata on abaxial epidermis of thermo-resistant cultivar were in close state, hut stomata of thermo-sensitive cultivar usually were in open state.2.The thermo-resistant cultivar had more xeromorphic features than the thermo-sensitive cultivars.Leaf anatomical structure showed that mesophyll cells of thermo-resistant cultivar arranged tightly and there were more and larger vessels in vascular bundle of lateral vein.The intercellular space in the mesophyll cells of sensitive cultivar and vascular systems were not fully developed and some spongy parenchyma cells showed severe plasmolysis.