This study focuses on the characterization of porous Vycor membranes modified by chemical vapor deposition of boron nitride (B-N-C-H) for gas separation. The B-N-C-H films were deposited on mesoporous Vycor tubes using triethylamine borane complex and ammonia as precursors. The effects of deposition temperature and reactant flow geometry on permselectivity of membranes with respect to various permeant gases were investigated. High selectivities (up to 50,000) were achieved between small molecules (He, H-2) and large molecules (N-2, Ar, C6H5CH3). The measured activation energies for the He and H-2 permeability are 9.5 kcal/mol and 12 kcal/mol, respectively. The membranes synthesized at lower temperatures and lower ammonia flow rates showed good mechanical and chemical stability.