Effect of mannan oligosaccharide (MOS) supplementation on growth and production performance of broiler chickens was evaluated by distributing 180 unsexed Cobb-400 chicks of 7 days old to 18 floor pens (10 birds in each) following completely randomized design and assigning six pens to each of the three dietary treatments viz., M0 (control; basal diet without MOS supplementation), M0.5 (basal diet with 0.5% MOS) and M1 (basal diet with 1% MOS) and managed uniformly for next 5 weeks. The final body weight and weight gain was significantly higher (P<0.05) in M0.5 as compared to M1 and M0. Average feed intake remained similar and consequently, significantly better feed conversion ratio (FCR) was found in M0.5 over control M0 and M1. Cost of production was lower (P<0.05) in M0.5 over M0 and M1. Supplementation of diet with 0.5% MOS in the poultry ration was found better in terms of growth, feed intake, FCR and cost of production.