||The present study was designed to overcome heat stress in Japanese quails through potassium chloride, sodium bicarbonate and vitamin C solution in calculated amount in water on thermo tolerance, histopathology and hematology of quails exposed to heat stress: This experimental trial was carried out at Avian Research and Training Centre (ARTC), UVAS Lahore and tests were performed at Department of Pathology UVAS, Lahore. There were three replicates in each treatment group and each replicate was of twenty quails, each group was comprised of 60 birds. The body weight of each the bird was. recorded on weekly basis. Blood samples were collected on the 21, 22, 23, 24, 29, 30 and 31 days of treatment from each group to evaluate the serum potassium and bicarbonate level in the blood. For hematological parameters the blood samples were collected on 22, 28 and 31 day of treatment and the vital organs for histopathology were collected after slaughtering 3 birds from each group. The hematological parameters were studied and the data was analyzed by two ways ANOVA. Group A quails revealed significantly higher weight gain than those of group B, but no significant difference was observed, when all groups were compared. Significantly less weight gain was revealed by the quails of group B, when compared to all other groups. Comparison between groups A, C, D, E, F and G was non significant. The highest FCR was exhibited by the birds of group A while the group B showed the poorest FCR. Better FCR was exhibited by group C, D, E, F and G. Serum samples were obtained from each group, for bicarbonate and potassium determination by spectrophotometric method. Group A, C, E, F and G exhibited a significantly higher serum potassium level than those of groups B and D. A significantly higher bicarbonate level was revealed in the serum of group A, D, E, F and G as compared to group B and C, on day 23 and onwards. But no significant difference was observed in serum of groups A, D, E, F and G. Blood hematology revealed no significant difference in red blood cells of groups A, C, D, E, F and G. Group B exhibited a significant lower values of red blood cells, packed cell volume, basophils, monocytes and showed a significant increase H/L ratio and eosinophils when compared to all other groups. Histopathological studied showed infiltration of heterophils, hyperemia, congestion of liver, heart and adrenal gland. It is concluded that, quails of group B (kept in high environmental temperature) revealed a decreased weight gain, poorest FCR, decreased serum potassium and bicarbonate level, decrease in hematocrit, monocytes and basophils and increased in eosinophils and H/L ratio. Supplementation of electrolytes and vitamin C (125 mg/L KC1, 75 mg/L NaHCO3 and vitamin C 62.5 mg/L) in water effect on heat stressed quails exhibited the better results in term of weight gain, serum electrolytes, blood profile and histology than those quails kept in heat stressed condition with no supplementation. From the present results it is concluded that 125 mg/L of KCI, 75 mg/L of NaHCO3 and 62.5 mg/L of vitamin C solution in water, alone or in combination may be used in quails to combat the effect of high ambient temperature and heat stress.