Functionalized cubic Ia3d mesoporous silica (FCIMS) with glycidoxypropyl groups was prepared and characterized by powder XRD, N2 adsorption, TGA, FT-IR spectroscopy, solid state 13C NMR spectroscopy and TEM, and studied as the support for the immobilization of Penicillin G acylase (PGA). The results show that the glycidoxypropyl groups have been chemically bonded to the silicon atoms on the surface of cubic Ia3d mesoporous silica (CIMS). The FCIMS materials possess the mesoporous structure with pore diameter of 8 nm which is ∼ 1 nm less than that of CIMS (9 nm). The influence of the amount of glycidoxypropyl groups on the initial specific activity and operational stability of PGA immobilized on FCIMS were examined for the hydrolysis of penicillin G potassium salt. The results show that PGA has been successfully immobilized covalently on the FCIMS materials, and the initial specific activity of PGA/FCIMS is 835 IU g–1 and PGA/CIMS is 624 IU g–1. After repeated use for 10 times, PGA/FCIMS retains 72 % of its initial specific activity and PGA/CIMS retains only 58 %.