Abstract: This study has been conducted to evaluate the use of Bio-Mos®, mannan oligosaccharide derived from the cell wall of yeast, as a potential replacement of growth promoting antibiotics in the diet of broilers. Effects of an antibiotic growth promoter (Avilamycin) and mannan oligosaccharide (Bio-Mos®) on performance have been examined in 320 days-old Ross 308 broiler chicks. These chicks were randomly grouped into two treatments with eight replicates of 20 chicks each. Commercial corn-soybean based broiler starter, grower and finisher diets were formulated as basal diets. Basal diets were supplemented with an antibiotic growth promoter (0.1% Avilamycin) and a mannan oligosaccharide (starter 0.15%, grower 0.1%, finisher 0.05% Bio-Mos®). Live weight, weight gain and feed intake, feed conversion ratio were not affected significantly by dietary treatments throughout the experiment (p>0.05). Mortality rate, hot carcass yield and feed cost for kg live weight gain did not show any significant differences among the groups (p>0.05). Mannan oligosaccharide (Bio-Mos®) has the potential to be an alternative to antibiotic growth promoters in broiler diets.