This study investigated the single and combined effects of pre- and probiotics supplement on the growth performance and immune response of rainbow trout. Seven diets supplemented with 1% Enterococcus faecalis (E), 0.4% mannan oligosaccharides (M) and 1% polyhydroxybutyrate (P) in single (E, M and P diets), double (EM and EP diets) or triple combinations (EMP diet) were fed to juvenile rainbow trout (13.2±0.25 g) for 12 weeks. During the feeding test, the fish were healthy and no mortality occurred. Although weight gain and specific growth rate (SGR) were significantly higher (P<0.05) in the fish fed single supplementation of mannan oligosaccharides, its combined supplementation together with E. faecalis showed further improvement of growth as well as feed gain ratio (FGR). On the other hand, single administration of E. faecalis could not improve any growth performance parameter. In addition, E. faecalis improved the immunological parameters such as hematocrit value, phagocytic index and activity and mucus production when administrated alone or combined with mannan oligosaccharides. After fourteen days challenge test the lowest cumulative mortalities were recorded in the fish fed E, M, EM and EMP diets. A single supplementation with E and M and combination of them improved the growth performance and immune response of rainbow trout.