A study was conducted to determine the effect of dietary ascorbic acid (AA) supplementation on performance of growing Japanese quails (Coturnix coturnix japonica) reared under high environmental temperatures (heat stress). Three hundred and fifteen (315) two-week old male and female Japanese quails were randomly divided into five groups of equal numbers and fed ad libitum on a maize/soyabean based diet meal. The meal were supplemented with AA at graded levels of 0, 50,100,150 and 200mg/kg diet and labeled groups 1,2,3,4 and 5 respectively. The birds were reared under maximum environmental temperature of 36.330 C and maximum relative humidity of 64 %. The results of the study demonstrated significant (P < 0.05) increase in feed intake and protein intake of all quail on AA supplemented diets compared with the non-supplemented group. However, there was no corresponding increase in feed and protein conversion ratios of quails fed AA supplemented diet. Birds exposed to heat stress and given AA diets had similar body weight gain with birds on AA free diet. The carcass yield was not significantly different between any of the five groups. There was also no significant different between any of the groups in red blood cell (RBC) count, haemoglobin (Hb) concentration, packed cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC) and total protein. It was concluded that the quails appeared to exhibit some level of resistance to heat stress, dietary supplementation of quail diets with up to 200 mg AA per kg was not necessary and not economically advantageous.