This dataset describes a label-free quantitative proteomic analysis of the extracellular secretome of the basidiomycete fungus Leucoagaricus gongylophorus LEU18496, GenBank: KJ419350.1, the obligate symbiont of leaf-cutter ants. The fungus was cultivated under different carbon sources to investigate substrate-dependent changes in protein secretion. Culture supernatants were collected at defined time points and analyzed by LC-MS/MS. The resulting dataset provides insights into the enzymatic repertoire involved in plant biomass degradation, including carbohydrate-active enzymes, oxidoreductases, and proteases, and contributes to the understanding of fungal adaptations to complex polysaccharide substrates.