Acylase I from Aspergillus melleus was immobilized on supports consisting of unmodified and modified silica. Modification was performed using 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde (GA). The effectiveness of immobilization was investigated using the standard Bradford method in addition to a number of physicochemical techniques, including spectroscopic methods (FTIR, Si-29 and C-13 CP MAS NMR), porous structure and elemental analysis, and zeta potential measurement. A determination of catalytic activity was made based on the deacetylation reaction of N-acetyl-l-methionine. Furthermore, the effect of pH and temperature on the catalytic activity of the free and immobilized enzyme, as well as the reusability of the silica-bound aminoacylase, were determined. The immobilized systems demonstrated a high degree of catalytic activity. The best catalytic parameters were those of aminoacylase immobilized on silica modified with APTES (apparent activity 3937 U/g, relative activity 61.6%). (c) 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:767-777, 2018