Prebiotics are non-digestive food ingredients which beneficially affect the host by selectively stimulating the growth and activity of health-promoting bacteria in the intestinal tract. This experiment was conducted to evaluate the effect of dietary supplementation of galactooilgosaccharide on the growth performances, survival and several of innate immunity parameters of rainbow trout (Oncorhynchus mykiss) larvae for 60 days. In this experiment, 360 of larvae (with average weight of 0.13±0.01g) in 4 treatments and 3 replicates (n=30 in each replicate) in a completely randomized design was divided and fed with diets containing 0, 1, 2 and 3 percent galactooligosaccharide respectively. The present results showed that highest WG, SGR and PER were observed in the diet containing 2 and 3 percent of dietary galactoologosaccharide which had a significant difference compared with other treatments (p<0.05). The highest, survival, total protein, albumin and globulin levels were observed in treatments containing 2 percent of dietary galactooligosaccharide which showed a significant difference compared with other treatments (p<0.05). Finally, the present results suggest that diets containing 2 percent of dietary galactooligosaccharide could improve growth, survival and innate immunity responses of rainbow trout.