A new room temperature ionic liquid (RTIL) has been prepared by directly Mixing InCl3 and 1-ethyl-3-methylimidazolium chloride (EMIC) under dry nitrogen atmosphere. The phase diagram of the binary system InCl3-EMIC was determined by DSC. Both Raman scattering and ab inito calculations indicate that InCl4- is the predominant indium-containing species in the ionic liquid. And it was further confirmed by NMR experiments.