This work investigated the impact of partially substituting soybean meal protein with defatted black soldier fly larvae (DBSFL) meal protein on performance parameters, carcass traits, meat chemical composition, cecal microflora, and economic efficiency in growing Muscovy ducks. Five dietary treatments were established, consisting of a basal control and four replacement levels in which DBSFL meal protein replaced SBM protein at 20%, 40%, 60%, and 80%. These treatments utilized 100 one-week-old ducklings, randomly distributed across four replicates of five birds each. The experimental duration was extended for 56 days. The 20% and 40% substitutions significantly improved performance parameters (p<0.05). Carcass traits and abdominal fat percentage also increased notably (p<0.05) in the DBSFL meal groups. The proximate composition of the meat showed no significant differences, except for crude protein, which increased significantly. The concentrations of meat cholesterol and triglycerides were significantly reduced (p<0.05) in the treated groups. The addition of DBSFL meal significantly (p<0.05) decreased harmful bacteria such as E. coli and Salmonella, while also notably (p<0.05) boosting beneficial bacteria in the ducks' cecum. The monetary value of the diets improved with the addition of the DBSFL meal. Substituting soybean meal protein with DBSFL meal protein, especially at 20%, enhances performance, meat nutritional quality, carcass traits, and gut microbiota, confirming DBSFL meal as a viable alternative protein supplement.