Extracellular secreted proteins by Aspergillus oryzae grew in yeast extract, malt extract, peptone and glucose (YMPG) were identified using mass spectrometry methods to determine reductase protein(s) in the fungal filtrate that might be responsible for reductase reactions, such as silver nanoparticles (SNPs) formation. FAD dependent oxidoreductase was one of the most prominent protein bands. This protein's structure is still unknown, so searching through the protein data bank (PDB) revealed that chain A, cyclohexylamine oxidase from Brevibacterium oxydans IH- 35a is the closet protein's structure to our identified protein. Our findings confirm that it is an extracellular soluble protein that contains a flavin-adenine dinucleotide (FAD) legend which might be playing an essential role in reduction processes performed by that fungus extracellularly