Birds reduce their food intake by the exposure to high ambient temperature (HT) which ultimately affects their productivity. However, physiological and behavioral responses of young chicks of different ages to HT have not yet been investigated. In this study, we examined the effects of HT (40°C, 4-h) in 3-, 5-, 7-, 14- and 21-d old chicks. There were no significant differences in food intake between heat exposed and control chicks up to 7-d old, while clear suppressions of food intake were observed in 14- and 21-d old heat exposed chicks. Body weights were not affected in all age groups; however, rectal temperature was significantly increased in almost all ages. We examined blood metabolites of 7-, 14- and 21-d old chicks and found that plasma glucose concentration gradually increased in 14- to 21-d old heat exposed chicks. Conversely, triacylglycerol age-dependently decreased during exposure to HT. No significant changes were detected in plasma total protein, uric acid and calcium investigated in 7-, 14- and 21-d old heat exposed chicks compared to control groups. However, plasma glutamic-oxalacetic transaminase showed a significant interaction between HT and age, implying that liver and/or heart was damaged by HT with aging. These results indicate that HT (40°C; 4-h) suppresses food intake in young chicks of 14- or 21-d old age which reflects in some of their plasma metabolic concentrations.