A quantitative structure–property relationship study of the infinite-dilution activity coefficients for a set of 38 organic compounds in ionic liquids such as 1-methyl-3-ethylimidazolium bis((trifluoromethyl)sulfonyl)imide, 1,2-dimethyl-3-ethylimidazolium bis((trifluoromethyl)-sulfonyl)imide, and 4-methyl-N-butylpyridinium tetrafluoroborate. QSPR study was carried out using the CODESSA PRO program. A general three-parameter QSPR model was obtained. Three orthogonal theoretical molecular descriptors satisfactorily correlate with the activity coefficients. The descriptors, such as the complementary information content, the fractional partial negative surface area and the count of hydrogen donor sites describe the dilution process in ILs.