Solubility and adsorption of high pressure carbon dioxide (CO,) to poly(styrene) (PS) were measured at 313.2 K and pressures up to 17 MPa using a quartz crystal microbalance (QCM) as a detector. Two kinds of PS film, made by dip coating (d-PS) and plasma polymerization (p-PS), were used as samples. The amount of adsorption onto both films was almost the same within the experimental range. The solubility to both films increased almost linearly against activity of CO2 up to unity, and that to p-PS was slightly higher than that to d-PS. Above unity, the solubility to p-PS film increased with the increase in activity. In contrast, solubility to d-PS sharply decreased near the unity and became a constant value.