For use in room-temperature electrodeposition of magnesium（Mg）metal, aging variation was studied to assess the electrochemical properties of a mixed system: an ionic liquid（IL）and a Grignard reagent. Cyclic voltammograms of a mixture of an IL, i.e. trimethylhexylammonium bis（trifluoromethylsulfonyl）amide（TMHA-Tf₂N; Tf＝CF₃SO₂）, and a Grignard reagent, i.e., ethylmagnesium bromide（EtMgBr）in tetrahydrofuran（THF）, showed redox currents for Mg metal deposition and dissolution. Similarly to other IL-Grignard mixed electrolyte solutions, the mixture examined in this study was found to have larger redox current than neat Grignard electrolyte solutions. Voltammograms for one-day-aged TMHA-Tf₂N-EtMgBr-in-THF mixtures showed smaller or almost no redox current. Furthermore, adding a Grignard reagent to the one-day-aged IL-Grignard mixture did not improve the electrochemical properties. Therefore, redox property deterioration was not attributable to a sizable decrease in the electrochemically active species or a shift of the Schlenk equilibrium in 2EtMgBr ↔ Et₂Mg＋MgBr₂. From our results, we speculate that Lewis acidic IL cations and Lewis basic Grignard species reacted gradually to form redox-inactive species or inhibitor（s）for the electrochemical deposition of Mg.