Abstract: Effect of dietary Mannan Oligosaccharide (MOS; activeMOS®) on growth, survival, body composition and some hematological parameters in carp (Cyprinus carpio) Juvenile were investigated for 45 days. Basal diet were supplemented with 0 (Control), 1.0, 2.0 and 3.0 g kg-1 MOS in a totally randomized design trial in triplicate groups. The experiment carried out in 100 L PVC tanks. About 20 juvenile carp with initially average weight 1.3±0.17 g were stocked in tanks and fed up a day. There were no significant differences in growth and feeding parameters between fish fed control and MOS supplementation diets (p>0.05). The highest and the lowest growth performance were observed in 1.0 g kg-1 MOS and control treatment, respectively. There were no significant differences in survival rate and body composition among experimental groups (p>0.05). But, in group treated with 1.0 g kg-1 MOS showed higher protein carcass (p>0.05) than other group. An elevation of hematocrit, lymphocyte (p<0.05), WBC, RBC, Hb and eosinophil (p>0.05) were found in the fish fed diet 1.0 g kg-1 MOS. The result indicated that 1.0 g kg-1 MOS can improved growth performance, survival, final production and some blood parameters of carp juvenile and it is appropriate for supplementation in the diet of cultured juvenile carp.