The purpose of this study was to investigate the effects of foliar spraying with hydrogen peroxide on the growth and flowering of chrysanthemum plants during periods of high temperature stress, with the aim of reducing damage caused by elevated temperatures. The experiment was conducted from July 4 to October 15, 2022, and involved three chrysanthemum cultivars: ''Pulkista'', ''Borami'', and ''Pinkyrang''. The results indicated that foliar spraying with hydrogen peroxide effectively reduced leaf temperature in all three cultivars. The treatment with 0.35% hydrogen peroxide at 13:00 showed the lowest stress level, with a difference of -5.3℃ between leaf temperature and air temperature in the ''Borami'' cultivar. In terms of growth characteristics, the foliar spraying of 0.35% and 0.175% hydrogen peroxide resulted in improvements in plant height, stem thickness, number of leaves, and leaf thickness across all three cultivars. Additionally, there was an interaction observed between the hydrogen peroxide treatment and cultivars in terms of plant height. However, regarding flowering characteristics, the hydrogen peroxide foliar spray treatment did not significantly delay flowering due to high temperatures or prevent the deterioration of flower color. The flowering period was approximately 1 to 2 days earlier than the control group, and the ''Pinkyrang'' cultivar treated with 0.35% hydrogen peroxide exhibited flower color that was closest to the original color. Notably, the incidence of deformities was lower in the hydrogen peroxide treatment group compared to the control group, and no deformities occurred in the ''Pinkyrang'' cultivar treated with 0.175% hydrogen peroxide. Regarding root activity, the formazan content was highest in the 0.35% hydrogen peroxide treatment group compared to the control group in all three cultivars. Although there was no statistically significant difference, the chlorophyll a content tended to be higher at 0.35% hydrogen peroxide treatment in all three cultivars. The carotenoid content was higher in the ''Borami'' cultivar compared to the control group. In terms of photosynthetic characteristics, the light saturation point was high at 0.35% hydrogen peroxide treatment, and the photosynthetic rate at high temperatures was high in all three cultivars treated with hydrogen peroxide. These findings suggest that foliar spraying of 0.35% hydrogen peroxide during chrysanthemum cultivation in high-temperature periods can reduce damage caused by elevated temperatures by lowering leaf temperature, improving root activity and photosynthetic ability, and enhancing heat resistance.