The solubility and diffusivity of carbon dioxide (CO2) in the solid-state isotactic polypropylene (iPP) were studied by using the pressure-decay method at temperatures of 373.15, 398.15, and 423.15 K and pressures ranging from 1 to 15 MPa. The solubilities of CO2 in the solid-state and amorphous regions of iPP were both obtained. They increased almost linearly with increasing pressure and decreased with increasing temperature. The Sanchez-Lacombe equation of state (S-L EOS) correlated the solubility in the amorphous regions of the solid-state iPP within 3% average relative deviation in conjunction with a temperature-dependent interaction parameter. The diffusion coefficient of CO2 in the solid-state iPP showed a weak concentration dependence and had an order of magnitude of 10(-10)-10(-9) m(2)/s in the solid-state iPP.