In aquaculture, functional feed formulation is an optimal solution of reducing high feed cost in an environmental friendly way; by replacing animal origin ingredients with plant based sources and functional additives. In the present study, effects of functional feed having 75% fish meal replacement with fermented or non-fermented soybean meal (supplemented with lysine & methionine) with two probiotic levels (2% & 4%) were investigated with reference to growth response, innate immunity, digestive enzyme activity and body composition of Nile tilapia for 16 weeks in laboratory conditions. Nile tilapia received 35% CP feed as T0 (containing 100% fishmeal), T1 (75% fermented soybean meal (FSBM) replacement and 2 % probiotics), T2 (75% non-fermented soybean meal (SBM) replacement and 2% probiotics), T3 (75% FSBM replacement and 4 % probiotics), T4 (75% SBM replacement and 4 % probiotics). The observed weight gain was 14.1 g in T0, 8.7g in T1, 8.4 g in T2, 9.38 g in T3 and 9.96 g in T4. The better value of FCR (1.88) was observed in T0 group and the maximum value of SGR (1.9) was also observed in T0. The WBCs count and IGM were highly reduced in non-fermented soybean groups. However, FSBM showed significant increase in WBCs count and IgM. Highest level of WBCs counts and IGM was observed in FSBM+ 4% probiotics. IgM level of O. niloticus was 10.13 mg/ml in T0, 9.76 mg/ml for T1, 9.30 mg/ml in T2, 11.36 mg/ml in T3 and 10.43 mg/ml in T4. The results of the digestive enzyme activity with non-fermented SBM had negative effect on digestive enzyme activity. Fermented soybean groups showed an improvement in digestive enzyme activity in comparison to non-fermented groups but not comparable to control group. Lipase activity of O. niloticus was 196.6 U/mg for T0, 190.30 U/mg for T1, 186.30 U/mg for T2, 190.21 U/mg for T3 and 186.2 U/mg for T4. Amylase activity was 4.46 U/mg for T0, 4.40 U/mg for T1, 4.56 U/mg for T2, 4.26 U/mg for T3 and 4.50 U/mg for T4. Protease activity was 71.04 U/mg for T0, 68.51 U/mg for T1, 64.42 U/mg for T2, 68.54 U/mg for T3 and 64.54 U/mg for T4. The results of present study indicated that FSBM had no significant effect on the proximate body composition with respect to moisture content, protein, fat and ash content, however crude protein and fat level were significantly decreased in non-fermented SBM groups. The levels of crude protein of O. niloticus were 16.05% for T0, 16.05% for T1, 13.54% for T2, 16.02% for T3