In this work, mixtures of 1-butyl-3-methylimidazolium chloride ([bmim]Cl) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide abmim][Tf2N]) were chosen to study because [bmim]Cl is suitable for processing biomass and [bmim][Tf2N] is suitable for increasing carbon dioxide(CO2) solubility in the ionic liquid phase. Solubilities of CO2 in mixed ionic liquid systems ([bmim]Cl and [bmim][Tf2N]) were measured at (353-393) K and at pressures up to 15 MPa with a magnetic suspension balance technique. Mixed ionic liquids were prepared at mole ratios, [bmim]Cl: [bmim][Tf2N] of 0.75: 0.25, 0.50: 0.50 and 0.25: 0.75. CO2 solubility in mixed ionic liquids changed regularly from that in single [bmim]Cl to that in single [bmim][Tf2N]. By assuming mixed ionic liquids as a mixture of two ionic liquids, the se-modified Sanchez-Lacombe equation of state could predict CO2 solubility data with pure component parameters of single ionic liquids and interaction parameters for [bmim]Cl-CO2, [bmim][Tf2N]-CO2 and [bmim]Cl-[bmim][Tf2N] to within an average relative deviation of 2.4%. (C) 2017 Elsevier B.V. All rights reserved.