Densities and viscosities of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmini][BF4]) (1) + N-methyl-2-pyrrolidone (NMP) (2) with w(1) = 0.0000, 0.5000, 0.6999, 0.8981, and 1.0000 at T = (298.15 to 318.15) K were measured and fitted to standard equations. The results show that densities and viscosities of the hybrid solvents decrease with the increase of temperature and mass fraction of NMP. A high-pressure variable-volume view cell technique was used to determine the solubility of CO2 in pure solvents and mixtures under elevated pressures up to 6 MPa at temperatures from (298.15 to 318.15) K. The results indicate that the solubility of CO2 in the pure solvents and mixtures increases with the increase of pressure and with the decrease of temperature. The solubility of CO2 in the mixtures increases with the increase of the mass fraction of NMP, but it is very close to that in pure [bmim][BF4] as the mass fraction of NMP is around 0.1019.