In this research, we report a new application of alternating-current electroluminescent (AC-EL) devices for carbon dioxide (CO2) detection at room temperature. The EL structure was designed for gas-sensing applications by replacing a dielectric layer with a graphene gas-sensing layer. The graphene-based EL gas sensor was fabricated by screen-printing of a ZnS:Cu,Cl phosphor layer and drop-coating of graphene synthesized by chemical vapor deposition (CVD) process. Optical characterizations confirmed that the graphene-based EL gas sensor showed similar optical properties to a typical AC-EL display device. From gas-sensing results, the AC-EL gas sensor exhibited high response to CO2 in concentration range of 100-1000 ppm at room temperature and high selectivity against NH3, C2H2 OH and C7H8. Furthermore, the EL gas sensors offer good repeatability, reproducibility and measurement accuracy. A sensing mechanism of AC-EL gas sensor was explained based on the resistance change of graphene sensing layer via a direct charge transfer process. These results could pave the way to develop a new type of gas sensor based on an EL principle.