The thermodynamic stability and kinetic inertness represent substantial obstacles for direct chemical transformation of CO2. Consequently, conversion of the CO2 equivalent in an efficient and energy-saving manner has gained much attention being viewed as an indirect pathway to chemical utilization of CO2. In this article, we would like to report the synthesis of oxazolidinones via the carboxylative cyclization of anilines with cyclic carbonate using protic ionic liquid 1,8-diazabicyclo[5.4.0]-7-undecenium imidazolide [HDBU][Im] as the bifunctional catalyst under mild conditions without addition of conventional organic solvents. The distinguished features of this protocol include low catalyst loading, wide functionality tolerance and convenient recycling of the catalyst. A series of functional groups such as -Cl, -Br, -CH3, -OCH3 and -NO2 can be well tolerated under the reaction conditions, providing the corresponding products in moderate to good yields (61-92%). In addition, to shed light on the cooperative interactions of [HDBU][Im]/EC and [HDBU][Im]/aniline, NMR technique and DFT study were also performed, respectively.