An effective separation of CO 2 from H 2 can be achieved using currently known polyethylene oxide (PEO)-based membranes at low temperatures but the CO 2 permeability is inadequate for commerical operations. For commercial-scale CO 2/H 2 separation, CO 2 permeability of these membranes must be significantly enhanced without compromising CO 2/H 2 selectivity. We report here exceptional CO 2/H 2 separation properties of a nanohybrid membrane comprising polyethylene glycol methacrylate (PEGMA) grafts on an organic-inorganic membrane (OIM) consisting of a low molecular weight polypropylene oxide (PPO)-PEO-PPO diamine and 3- glycidyloxypropyltrimethoxysilane (GOTMS), an alkoxysilane. The CO 2 gas permeability of this nanohybrid membrane can reach 1990 Barrer with a CO 2/H 2 selectivity of 11 at 35°C for a mixed gas mixture comprising 50% CO 2 - 50% H 2 at 3.5 atm. The transformation of the inorganic silica phase from a well-dispersed network of finely defined nanoparticles to rough porous clusters appears to be responsible for this OIM membrane exceeding the performance of other state-of-theart PEO-based membranes.