Thermo-responsive membranes were prepared by fabricating cross-linked poly(N-isopropylacrylamide) (PNIPAM) hydrogels inside the pores of porous Nylon-6 (N6) membranes by the free radical polymerization method. SEM micrographs of the prepared membranes showed that PNIPAM hydrogels were filled uniformly throughout the entire thickness of the porous N6 membranes. Both PNIPAM-filled N6 membranes prepared at 60 degrees C and at 25 degrees C exhibited significant reversible and reproducible thermo-responsive diffusional permeability. When the environmental temperature remained constant, the diffusional coefficient of vitamin B-12 (VB12) across the PNIPAM-filled N6 membrane prepared at 25 degrees C was ca. twice the value of that prepared at 60 degrees C due to different filling yields. The thermo-response factor of the membrane prepared at 25 degrees C was higher than that prepared at 60 degrees C. The 3-dimensional interpenetrating network structure of the cross-linked PNIPAM hydrogels inside the N6 porous substrates could effectively ensure a repeatable thermo-responsive permeation performance.