The study was conducted to assess the effects of using Galleria mellonella larvae (GML) as an unconventional protein source (insect protein) replacing soybean meal (SBM) in the Nile tilapia diets. Approximatley 180 fish (with an initial average body weight of 5.6±0.18g) were randomly assigned among 12 experimental aquariums, with 15 fish per aquarium, giving three replicates of 45 fish for each treatment. GML replaced 0, 5, 10, and 15% of the soybean meal, which constituted 40% of the control diet. These replacements were corresponding to 0, 20, 40, and 60g/ kg for diets D1, D2, D3, and D4, respectively, for 56 days. All test diets were designed to be iso-nitrogenous. At the end of the experiment, growth productivity, feed utilization, body composition, biochemical analysis, immune parameters and economical evaluation were examined.  The results indicated that, metrics such as FW, TBWG, ADG, SGR, and SR showed improvements in diets D2, D3, and D4, with a mortality rate of 6.67% in the control group (D1) and 0% in the other treatments. Fish fed on GML diets D2, D3, and D4 demonstrated a significant (P< 0.05) increase in FI, FCR, CPI, PER, energy retention percentage and lysozyme activity in all treatment groups compared to the control, whereas there were non-significant changes (P˃ 0.05) in ALT, AST, glucose, and cholesterol. Additionally, feed formulation costs decreased, with net improvements in the feeding cost percentages of 6.17, 8.70, and 10.07% for diets D2, D3, and D4, respectively, compared to the control group. The study revealed that using GML as an insect protein holds great potential as a substitute for SBM feeds to increase the production of the Nile tilapia.