The synthesis of Triphenylphosphonium trichloroiodoaluminate (III) ionic liquids (ILs) is reported here. The product was characterized by spectroscopic and analytical methods such as 31P-NMR, FT-IR, cyclic voltammetry, CHN, TGA and differential thermal analysis (DTA). Thermal analyses were used to investigate the thermal behavior of this compound. The results show that this ILs has excellent thermal stability below 110?C. Along with the experimental study; this compound has been studied computationally at the B3LYP/LANL2DZ level of theory using the Gaussian 98 program package. From these calculations, optimized geometries, molecular parameters, and vibrational spectra of ILs have been calculated. In addition, calculated frequencies are compared with the experimental frequencies after correction by the appropriate scaling factor. This comparison shows that our theoretical data are in good agreement with the experimental results.