BACKGROUND: Growth of population and food supply is one of the biggest problems in the world and aquaculture plays an important role in food production and supply for human beings. OBJECTIVES: The aim of this study was to evaluate the effect of commercial probiotic (Bactocell) and prebiotic (Manan) on the growth and immune parameters in rainbow trout. METHODS: Seven hundred and twenty fish were randomly divided into 6 groups with three replicates. The fish in the first group (control) were fed with commercial pelleted diet. The other five groups were fed with 100 mg of probiotic, 2.5 g (grams) of prebiotic, 5 g of prebiotic, 100 mg of probiotic and 2.5 g of prebiotic, and 100 mg of probiotic and 5 g of prebiotic per kilogram of food for 45 days, respectively. Then, all treatment groups were fed with usual food (without probiotic and prebiotic) for 15 days. Growth parameters were evaluated on days 0 and 60. Blood samples were collected for immunological experiments (level of Lysozyme, total antibody levels of serum, and activity of the complement system) on days 0, 15, 30, 45, and 60. RESULTS: All treatments fed with probiotic and peribiotic showed significant improvements (p<0.05) compared to the control group in terms of growth parameters including weight gain, special growth rate, and food conversion rate. The results of immunology also showed that fish fed with a combination of probiotic and peribiotic had a significant difference with other treatments and the control group (p<0.05). CONCLUSIONS: The use of Bactocell and Manan improved the growth and immune response of rainbow trout.