Liquid structures of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [BDMI+][TFSA(-)] and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)amide [BDMI+][TFSA(-)] were studied by large-angle X-ray scattering (LAXS) experiments to elucidate methyl substitution effect at the C2 position of imidazolium cation on the long-range ordering of the ionic liquids. Radial distribution functions for both ionic liquids showed that the intermolecular correlations of ca. 5.5 and 10 angstrom a e significantly different from each other, unlike that of ca. 15 angstrom. MD simulations were also performed. It turns out that the methyl substitution at the C2 position of imidazolium causes variation of the orientation of the nearest neighboring ion-ion interactions without significant changes in the long-range ordering, probably longer than 15 angstrom, of the ionic liquids.