This experiment was conducted to investigate the effects of various levels of organic acids and virginiamycin on performance, blood parameters, immunoglobulin and microbial population of broiler chickens. This trial was conducted in a completely randomized design using five treatments and four replicates. The dietary treatments included a control diet without additives, diets containing 0.05%, 0.10% and 0.15% mixtures of organic acids, and a diet containing virginiamycin as an antibiotic. Based on the results, there was no significant effect of the experimental diets on feed intake of the broilers during the starter period. However, at the end of the grower period and throughout the rearing period, feed intake was significantly improved by experimental dietary treatments. Moreover, diets including organic acids enhanced the microbial population of broiler gut. Thus, the current findings support the conclusion that organic acids improve productive traits and health status in broiler chickens.