The a minopropyl-functionalized silicas (APFS) with higher loading of amino groups was synthesized by the co-condensation of tetraethylorthosilicate (TEOS) and gamma-aminopropyltriethoxysilane (APTES) in W/O microemulsion. Thus synthesized APFS was characterized by FT-IR spectroscopy, thermogravimetry, element analysis, solid state C-13 and Si-29 MAS NMR, TEM, and N-2 sorption. The results show that the aminopropyl groups were condensed as the part of the silicate framework, and the amino contents could be adjusted by changing the volume ratio of APTES to TEOS in W/O microemulsion. APFS has been firstly used as the support for the immobilization of penicillin G acylase after activation with glutaraldehyde. Effects of the volume ratio of APTES to TEOS on the physico-chemical properties of APFS and the performance of immobilized penicillin G acylase were systematically investigated. Penicillin G acylase immobilized on APFS with the volume ratio of APTES/TEOS = 1/9 (1.77 mmol g(-1) amino groups) behaves higher specific activity of 2759 IU g(-1) and higher operational stability of 86% of the initial specific activity after recycled for 5 times, and the immobilization yield of 97%. (C) 2009 Elsevier B.V. All rights reserved.