Phase equilibria of carbon dioxide (CO2) + poly(methyl methacrylate) (PMMA-15 k, PMMA-120 k) + ethanol ternary systems were measured at temperatures ranging from (293.3 to 359.7) K and pressures up to 14.1 MPa. Furthermore, cloud point temperatures of PMMA + ethanol binary systems were determined at pressures up to 15 MPa. To determine the phase boundary, we observed the cloud points and bubble points by using a variable volume view cell. With the addition of CO2 into the binary PMMA + ethanol mixture, the upper critical solution temperature (UCST) line shifts toward higher pressure and temperature values. At high CO2 concentrations, the lower critical solution temperature (LCST) and UCST curves merge. Further, the liquid-liquid split phenomenon is observed over the entire temperature range.