Abstract: The objective of this study was to investigate the effects of heat stress on leaf and petiole's microscopical structure of different thermo-resistant cultivars of Raphanus sativus L.the results obtained are summarized as follows: Under heat stress, the studied thermo-tolerant cultivars showed higher stomatal density, smaller volume and smaller stomatal opening area on abaxial epidermis than that of thermo-sensitive cultivars.Moreover, we observed those thermo-tolerant cultivars have thicker leaf, denser palisade tissue and smaller stomatic chamber, With more developed vein and much less occurred plasmolysis.Compared to thermo-sensitive cultivar, the petioles of thermo-tolerant cultivar were more study along with more quantity and larger transportation area of vascular stand as well as more active cambium.Based on these phenomena,the relation between the different structure of thermotolerant and thermo-sensitive cultivars were discussed, function of keeping water to avoid injuring under heat stress being discussed as well.