This study investigated the effects of dietary prebiotics, probiotic, synbiotic and organic acid salt supplementation on broiler growth performance, intestinal microflora, and histomorphology. A total of 300 one-day-old broiler chicks were randomly assigned to 5 different treatments with 3 replicates including 20 birds each. The birds received the same basal diet based on the corn-soybean meal, and additives included in the diet at 0 control, prebiotic (1 g/kg), probiotic (1 g/ kg), synbiotic (1 g/ kg), and acidifier (5 g/ kg). The body weight, weight gain, feed conversion, intestinal morphology and microbiology of birds showed significant (p0.01) improvement with dietary pre, pro, synbiotic and organic acid salt supplementation from 0 to 21d, 22-42 d and from 0-41 d in comparison with the control group. Synbiotic followed by probiotic supplemented groups revealed the highest final body weight, weight gain, better feed conversion and the highest antibody response to Newcastle disease vaccine (NDV) vaccine in comparison with prebiotic and organic acids. Moreover, synbiotic followed by probiotic supplementation significantly improved intestinal morphology and intestinal microbial ecology than prebiotic, organic acids and control groups. In conclusion, we suggest the use of synbiotic followed by probiotic is preferable as efficient growth and health promoters for broilers in comparison with prebiotic and organic acids. Keywords: Prebiotic, Probiotic, Synbiotic, Organic acids, Broilers