In the present study, the effect of melatonin and sodium nitroprusside treatments on the improvement of high temperature tolerance in California Wonder green bell pepper plant was studied. For this purpose, a factorial experiment was conducted in a form of a completely randomized design in three replications at Zabol University's Faculty of Agriculture. In this research, green bell pepper plants of Wonder cultivar were exposed to different temperature treatments (25°C, 35°C and 40°C) for 24 hours after being sprayed (foliar application) with 0μM, 50μM and 100μM concentrations of melatonin and sodium nitroprusside. Results showed that Shoot dry weight without fruit (DWPWF) at 40°C in compared to 25°C, 21.54% decreased. Also, foliar application with 100μM melatonin in compared to control (0uM) caused a 13.26% an increased in dry weight of shoots without fruit (DWPWF). Also, leaf chlorophyll at 40°C temperature in compared to 25°C temperature 32.82% decreased and foliar application with 100μM melatonin and 100μM sodium nitroprusside improved leaf chlorophyll value in compared to other foliar application treatments. Foliar application with 50uM and 100uM sodium nitroperoxide at 40°C temperature caused decreased of 15.16% and 20.99% of leaf hydrogen peroxide in compared to 0uM foliar application treatment, respectively. Also, under 40°C temperature, foliar application with melatonin and sodium nitroprusside (50μM and 100μM) in compared to 0μM foliar application activity of leaf superoxide dismutase enzyme increased. Also, leaf nitrogen under with 50 μM and 100μM melatonin in compared to 0μM foliar application 9.61% and 23.72% increased. Leaf potassium in 40°C temperature, foliar application with 50uM melatonin, 100uM melatonin, 50uM sodium nitroprusside and 100μM sodium nitroprusside 55.20, 72, 25.60 and 70.40% in compared to 0uM foliar application increased respectively. leaf iron in foliar application with 100μM sodium nitroprusside in compared to 0μM foliar application 17.96% increased.