The present study was conducted to evaluate the effect of vaccination against Newcastle disease, infectious bronchitis and infectious bursal disease on some biochemical parameters in serum of broiler chickens. Two hundred and fifty Ross 1-day old unsexed broiler chicks were divided into two groups (unvaccinated and vaccinated), blood samples were obtained from each group weekly until 8 weeks old. The results revealed significant differences in values of some biochemical parameters according to various ages of chickens within either unvaccinated or vaccinated groups, the effect of different ages on parameters was more clearly observed in vaccinated group. It was also revealed from this study that vaccination had no effect on levels of glucose, total protein, total lipids cholesterol, triglycerides, high density lipoprotein-cholesterol (HDL-c) and low density lipoprotein-cholesterol (LDL-c) and the activity of alanine aminotransferase (ALT). Vaccinated chickens showed a significant reduction in the level of albumin, albumin/globulin ratio and alkaline phosphatase (ALP) activity accompanied with an elevation in the level of globulin and activities of aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) compared with their values in non vaccinated chickens. These data suggest the interference of age and vaccination in broiler chickens on some biochemical parameters.