Thirty-six growing V-line rabbits of both sexes, 5 weeks old, with initial weights of 791.7 ± 14.1 g were used for the study through summer season from June to September(2104). The rabbits were randomly allocated to four treatments groups of 9 rabbits each. Each treatment was further sub-divided into 3 replicate of 3 rabbits. Group one fed control diet free of feed additives and served as a control group. Group 2 and 3 supplemented with 400 and 800 mg dried onion / kg diet, respectively. Group 4 received control diet, but drinking water supplemented with 200 mg vitamin C / l water. Results showed that at 15 weeks of age the live body weight was significantly (P ≤ 0.05) increased by the addition of ascorbic acid and dried onion at different inclusion rate. A significant decrease in feed consumption was recorded in the group received diet supplemented with 800 mg onion / kg diet in comparison with the control group. Significant (P ≤ 0.05) improvement in feed conversion ratio was observed in dried onion or ascorbic acid groups in comparison with the control. Hematological parameters were insignificantly affected by treatments. Dried onion and ascorbic acid failed to induce any significant impact on sheep red  blood cells(SRBCs) in comparison with the control group. All feed additives significantly (P ≤ 0.01) reduced serum total lipids, triglycerides, total cholesterol and low density lipoprotein, however, they had insignificant effect on high density lipoprotein concentration in comparison with the control group. Malondialdehyde as an indicator of lipid peroxidation was significantly decreased in all treatments, however, only the group received 400 mg onion in their diet recorded significant (P ≤ 0.05) increase in total antioxidant capacity in comparison with the control group.  In conclusion, rabbit dietary supplementation with ascorbic acid or dried onion could have beneficial effects on performance under summer environment without any side effects.