Cluster formation of 1-dodecy1-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (Cumim+TFSA) in benzene solutions was investigated using small-angle neutron scattering (SANS), NMR, attenuated total reflectance infrared (ATR-IR), and large-angle X-ray scattering (LAXS) techniques. The SANS measurements revealed that Cumim+TFSA is heterogeneously mixed with benzene in the narrow range of benzene mole fraction 0.9 <= x(C6D6) <= 0.995 with a maximum heterogeneity at X(C6D6) approximate to 0.99. The NMR results suggested that the imidazolium ring is sandwiched between benzene molecules through the cation - pi interaction. Moreover, TFSA probably interacts with the imidazolium ring even in the range of x(C6H6) >= 0.9. Thus, the imidazolium rings, benzene molecules, and TFSA would form clusters in the C(12)mim(+)TFSA(-) benzene solutions. The LAXS measurements showed that the distance between the imidazolium ring and benzene is similar to 3.8 angstrom with that between the benzene molecules of similar to 7.5 angstrom A. On the basis of these results, we discussed a plausible reason for the liquid liquid equilibrium of the C(12)mim(+)TFSA(-) benzene system.