Excess molar enthalpies H-m(E) and excess molar volumes V-m(E) of (1,3-dimethyl-2-imidazolidinone + benzene, or methylbenzene, or 1,2-dimethylbenzene, or 1,3-dimethylbenzene, or 1,4-dimethylbenzene, or 1,3,5-trimethylbenzene, or ethylbenzene) over the whole range of compositions have been measured at T = 298.15 K. The excess molar enthalpy values were positive for five of the seven systems studied and the excess molar volume values were negative for six of the seven systems studied. The excess enthalpy ranged from a maximum of 435 J . mol(-1) for (1,3-dimethyl-2-in-ddazoline + 1,3,5-trimethylbenzene) to a minimum of -308 J . mol(-1) for (1,3-dimethyl-2-imidazoline + benzene). The excess molar volume values ranged from a maximum of 0.95 cm(3) mol(-1) for (1,3-dimethyl-2-imidazoline + ethylbenzene) and a minimum of -1.41 cm(3) mol(-1) for (1,3-dimethyl-2-imidazoline + methylbenzene). The Redlich-Kister polynomial was used to correlate both the excess molar enthalpy and the excess molar volume data and the NRTL and UNIQUAC models were used to correlate the enthalpy of mixing data. The NRTL equation was found to be more suitable than the UNIQUAC equation for these systems. The results are discussed in terms of the polarizability of the aromatic compound and the effect of methyl substituents on the benzene ring.