Some cucurbit plants (Cucumis sativus L., Cucurbita pepo L., Cucumis melo L. and Citrillus lanatus L.) were used for investigating some physiological changes and protein patterns under heat stress in plants. Leaf samples were exposed tohigh temperatures as follows 35, 40, 45, 50, 55 and 60°C. Percentage of ion leakage, chlorophyll content, leaf relative water content (RWC) and loss of turgidity, total soluble protein (TSP) content and protein profiles were determined in leaf samples kept at each temperature stage for 30 minutes. Ion leakage was increased especially 55 and 60°C in all cucurbits parallel to the temperature increasement. Total chlorophyll content was decreased slightly in both cucumber cultivars, zucchini, in both melon cultivars and watermelon due to high temperatures. The RWC of cucurbits was decreased on the contrary of the loss of turgidity, which was parallel to the increment of temperatures. While the TSP content in cucumber was decreased with temperature increasement, it was not changed in zucchini and watermelon. In melon cultivars TSP was not noticeably changed until 55°C, but significantly decreased at 60°C. When the SDS-PAGE profiles of cucurbits were examined, many protein bands were observed with sizes ranging from 6.5 kDa to 211 kDa.