In this study, usage possibility of mannanoligosaccharide in gilthead sea bream (Sparus aurata) and its effects on digestibility of nutrients were investigated. BioMos derived from the cell wall of bread yearst was used as mannanoligosaccharide. Fish with in.ll ± i3. 19 g average weight were stocked to 9 octagonal cages each of which was included 20,000 ±2io fish in three replicates.