Heat stress is the most major environmental element contributing to rabbit health problems and reduced production. It is proposed that essential oils be applied to alleviate heat stress-induced oxidative damage in rabbits. The purpose of this feeding trial was to determine the protective impact of pumpkin seed essential oil (PSO)–supplemented diets in reducing the threat of unambient temperature on growing rabbits. Five groups of 5-week-old rabbits were allocated randomly into separated galvanized wire battery. The first group was raised under normal conditions (18 ± 2 °C) and fed a control diet (control group; CNT), whereas the other four groups were exposed to high ambient temperature (38 ± 2 °C) and fed a control diet supplemented with 0 (PSO0.0), 0.5 (PSO0.05), 1.0 (PSO1.0), and 2.0 (PSO2.0) mL PSO/kg diet. Results indicated that all supplemented groups and the positive control have higher live body weight compared with the heat stress group (PSO0.0) at 9 weeks of age. Supplementing of PSO resulted in significant improvement in weight gain at 5–9 weeks and 9–13 weeks compared with PSO0.0 group. The highest feed intake was detected in PSO0.05 group compared with that in other groups. Both PSO2.0 and PSO2.0 groups showed the lowest feed conversion ration compared with other groups. Heat-stressed rabbits given a high dose of PSO (1 to 2 mL) had higher hemoglobin concentrations and lower white blood cell counts throughout the experiment than those given a control diet and subjected to heat stress. All hepatic and renal function parameters improved significantly in the rabbits fed a high dose of PSO as compared to the heat-stressed control group, while protein constituents were significantly higher in experimental groups fed 2 mL PSO compared with other groups. Heat-stressed rabbits administered graded amounts of PSO had the lowest plasma glucose, cortisol, thyroid, and corticosterone concentrations and were noticed to be equivalent to the control group fed unsupplemented diet and reared under normal conditions. The immunohistochemistry analysis demonstrated that rabbit groups reared under heat stress and given 2 mL PSO supplemented diets had negative caspase-3 immunoreactivity surrounding portal tract and normal structure. In conclusion, adding pumpkin seed oil up to 2 mL/kg diet for growing rabbits is indorsed to promote growth as well as antioxidant and immunological status under heat stress conditions.