Abstract: The study was conducted to investigate the effects of MannanOligoSaccharide (MOS) on internal organ weights, pHs of GastroIntestinal Tract (GIT) and carcass characteristics in broilers. A total of 120, 1-day-old Ross 308® chicks were used in this study. Birds were assigned into four groups, each consisting three subgroups which are having 10 animals in them. The control group was fed a basal diet without supplemented MOS and the treatment groups were fed 0.05, 0.10 and 0.15% MOS in basal diet. MOS addition to the diet did not have any effect on carcass characteristics in broilers. Pancreas weight was significantly (p<0.05) lower in 0.10% MOS supplemented group than those in control group. The weight of bursa of fabricius in 0.05% MOS supplemented group was significantly (p<0.05) higher than those in control group. PHs in crops of animals in MOS supplemented groups was higher than (p<0.05) those in control group. MOS addition to the broiler diet did not alter carcass parameters although, supplementation increased pancreas weight and decreased the weight of bursa fabricius. Additionally MOS in diet altered the pH of the crop.