Composite membranes comprised of a thin cationic poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) layer and a microporous polysulfone (PSF) substrate were prepared by coating a layer of PDMAEMA onto the PSF substrate. The homopolymer PDMAEMA was synthesized by free radical bulk polymerization using 2,2′-azobisisobutyronitrile as an initiator. The membrane morphology was examined under scanning electron microscopy. The effects of parameters involved in the membrane preparation procedure on the permselectivity of the resulting membrane were investigated. The permeability of the membrane to H2, N2, O2, CO2, and CH4 was tested, and the membrane showed a high permselectivity to CO2. For example, at 23 °C and 412 kPa of CO2 feed pressure, the permeance of CO2 was 30 GPU and the CO2/N2 ideal separation factor was 53. The high CO2/N2 permselectivity of the membranes make them particularly suitable for CO2 capture from flue gas, a system relevant to greenhouse gas emission control. The effect of temperature on the performance of the membrane was also evaluated.