A novel electrolyte system for a rechargeable magnesium battery has been developed. The electrolyte consists of ethylmagnesiumbromide in tetrahydrofuran (EtMgBr/THF) with an ionic liquid (IL) of quaternary ammonium salt. The ionic conductivity of the electrolyte with the composition of EtMgBr/THF:IL being 3:1 in volume was 7.44mScm−1 at 25°C. A reversible processes of cathodic deposition and anodic dissolution of magnesium has been successfully achieved in the mixed electrolyte system of EtMgBr/THF+IL at room temperature.