The objective of this study was to determine the effect of age on the response of enzyme activities in blood serum of growing broiler chickens. The research was conducted on Ross 308 chickens. Blood serum samples were collected three times at 14, 21 and 42 days of age. Significant effects of age were found for both aspartate aminotransferase (AST) and lactate dehydrogenase (LDH).There were no statistically significant age- dependent differences among alanine aminotransferase (ALT) and creatine kinase (CK). The results proved the effects of biochemical metabolic processes, resulting from selection for intensive growth in meat type chickens.