Here, we report that the ionicity of a protic ionic liquid (PIL) could be changed when it was mixed with a solvent. Ionicities of PIL 1-methylimidazolium-acetic acid in N , N -dimethyl formamide, dimethyl sulfoxide, tetrahydrofuran, diethyl ether, ethyl acetate, acetonitrile, acetone, and 1,2-dichloroethane have been investigated by a 1 H NMR-based method at 298.15 K. The ionicity of a neat PIL is 92.8%. It changed a little with adding a small amount of solvent; however, when the PIL was highly diluted, it could dramatically increase to nearly 100% in acetone and decrease to about 63.9% in dimethyl sulfoxide. Furthermore, some possible factors influencing the ionicities of these PIL solutions were discussed. This research highlights the solvent effect on the ionicity of a PIL solution and offers opportunities for designing a PIL solution.