MFI-type zeolite membranes were modified by depositing molecular silica at a small number of active sites in the internal surface by in situ catalytic cracking of silane precursor. The limited silica deposition reduced the effective size of the zeolitic channels that dramatically enhanced the H-2 selectivity without causing a large increase in H-2 transport resistance. The modified zeolite membrane achieved an extraordinary H-2/CO2 permselectivity of 141 with a high H-2 permeance of 3.96 x 10(-7) mol/m(2).s.Pa at 723 K. The effect of pore modification on the gas transport behavior was studied on the basis of single gas permeation data.