High quality nanocomposite B-MFI hollow fibers were successfully prepared by pore-plugging hydrothermal synthesis. The incorporation of boron into the MFI structure modifies the n-hexane/2,2-dimethylbutane vapor separation properties of the membranes, with the materials improving the n-hexane/2,2-dimethylbutane intrinsic separation factors of Al-MFI by a factor of 2 (up to a value of 200) at comparable conditions. The permeation performance of the membranes is essentially governed by a molecular sieving mechanism driven by preferential diffusion of n-C6 and configurational diffusion effects favoring n-hexane adsorption from n-hexane/2,2-dimethylbutane mixtures. A strong confinement scenario for surface diffusion of both n-hexane and 2,2-dimethylbutane seems to prevail.