Aromaticity and the important electronic configurations of uracil are studied by index of deviation from aromaticity (IDA) and CiLC (Cl/LMO/CASSCF) analysis. The calculated IDA values of uracil are 5.256 and 4.998 in gas phase and in solvent model, respectively. These large IDA values indicate that uracil is almost completely non-aromatic even in solvent. The CiLC analysis has revealed that main ionic electronic configurations of uracil involve charge transfer from endocyclic neighboring carbon atom to exocyclic oxygen atom. (C) 2015 Elsevier B.V. All rights reserved.