The permeations of pure CO2 and N-2 gases and a binary gas mixture of CO2/N-2 (20/80) through poly(dimethylsiloxane) (PDMS) membrane were carried out by the new permeation apparatus. The permeation and separation behaviors were characterized in terms of transport parameters, namely, permeability, diffusion, and solubility coefficients which were precisely determined by the continuous-flow technique. In the permeation of the pure gases, feed pressure and temperature affected the solubility coefficients of CO2 and N-2 in opposite ways, respectively; increasing feed pressure positively affects CO2 solubility coefficient and negatively affects N-2 solubility coefficient, whereas increasing temperature favors only N-2 sorption. In the permeation of the mixed gas, mass transport was observed to be affected mainly by the coupling in sorption, and the coupling was analyzed by a newly defined parameter permeation ratio. The coupling effects have been investigated on the permeation and separation behaviors in the permeation of the mixed gas varying temperature and feed pressure.