Effects of dietary synbiotics on growth performance, survival, stress resistance, body composition and immune response in the Caspian roach (Rutilus rutilus) were evaluated. Fish with an initial average weight of 4.14±0.25 g were randomly distributed into tanks (50 fish per tank) and triplicate groups were fed a control diet or diets containing 1 g kg^-1 and 2 g kg^-1 synbiotics. After an 8-week feeding period, a general enhanced growth performance and feed efficiency were observed in fish fed on the diet containing 2 g kg^-1synbiotics (p<0.05). Subsequently, immune responses (Ig levels, lysozyme activity and ACH50) were significantly higher in 2 g kg^-1 synbiotics fed fish (p<0.05). Although all levels of dietary synbiotics significantly increased resistance to a salinity stress challenge (p<0.05), the highest survival rate was observed in this group. The intestinal tract of the fish with synbiotic diet supplementation had higher concentrations of lactic acid bacteria (7.13±0.32 log CFU g^-1). The protein and lipid contents in the whole body increased in the 2 g kg^-1 synbiotics fed group. At the end of experiment the fish fed synbiotics had the highest survival index after 40 hours exposure to salinity stress (13.8 ppt). Results showed that the addition of synbiotics to the diet of Roach (Rutilus rutilus) stimulates the beneficial intestinal microbiota and alters their immune defense system.