In factorial arrangement of treatments (2×4), an experiment was conducted to evaluate the effects of stocking density and vitamin C, vitamin E and their combination on growth performance of Californian rabbits during summer season (high ambient temperature of 36.4 ◦C and maximum relative humidity of 97%). Sixty unsexed 7-week-old rabbits were distributed into 8 groups of three replications each. The rabbits were kept in battery cages at two stocking densities; 10 or 15 rabbits/m2 and were fed on four experimental diets; first group was fed the control diet. The other three experimental diets were formulated to contain vitamin C (0.5 g/kg diet), vitamin E (0.25 g/kg diet) or both at the same suggested levels. Growth trial lasted for 7 weeks. The tested criteria included live body weight, live weight gain, feed intake, feed conversion ratio, some blood metabolites and carcass characteristics. Low stocking density increased significantly final live weight, daily weight gain and feed intake. The concurrent administration of vitamin C and vitamin E significantly improved the final body weight, daily gain and feed conversion ratio of rabbits. However, stocking density did not significantly affect feed conversion, carcass traits or plasma blood parameters. The single or combined addition of vitamins C and E significantly increased the percentages of carcass yield and total edible parts. A significant reduction was observed in plasma albumin level due to added dietary vitamin E. The effect of interaction between added dietary vitamins and cage density did not significantly affect most of variables examined in the present study. It can be concluded that stocking density of 10 rabbits/m2 or combined addition of dietary vitamins C (0.5g/kg diet) and E (250 mg/kg diet) may improve rabbit performance during summer season.