MFI zeolite membranes having different Si/Al ratios were prepared by secondary growth of crystalline colloidal seeds under hydrothermal conditions. An MFI membrane of Si/Al=infinity showed a n-C4H10 permeance of 1.5X10(-5) m(3) (STP)m(-2) s(-1) kPa(-1) and a n/i-C4H10 selectivity of 15 at 150degreesC. By addition of Al into MFI membranes, the zeolite layers appeared to be randomly oriented, and n/i-C4H10 selectivities were decreased. Methylation of toluene using MFI catalytic membrane reactors was carried out at 400-500degreesC. Toluene conversions increased with reaction temperature and a maximal p-xylene selectivity of 80% was achieved. suggesting the effectiveness of MFI catalytic membrane reactors.