This study evaluated the efficacy of organic acids as a growth promoter for broiler chickens relative to antibiotic growth promoters (AGPs). Broiler chickens were supplemented with graded doses of an organic acid blend (OAB, 1 g and 2 g/kg diet) and bacitracin methylene disalicylate (BMD, 0.5 g and 1 g/kg diet) for 35 days. Supplementation of OAB improved (P < .001) feed conversion ratio (FCR) and increased protein accretion (P < .001). Dietary acidification caused pH of the gizzard to decline linearly (P < .01) with the dose of supplemental OAB. In the lower intestine, pH remained unaffected by dietary treatments. Unlike BMD, supplemental OAB selectively promoted growth of lactobacilli in the small intestine. Moreover, compared to BMD, OAB tended to maintain the villi in the small intestine at a greater height. Although benefits of exceeding the dose of supplemental organic acids more than 1 g/kg diet are not always conspicuous, based on the live weight and feed conversion data, supplementation of 2 g organic acid per kg diet may be recommended for total replacement of AGPs in broiler diet.