The aromaticity of benzenes annelated to small rings is studied through ab initio molecular orbital calculations. The aromaticity of benzene is defined in terms of the equivalent electronic states for six a bonds from a configuration interaction localized molecular orbital CASSCF (CiLC) analysis on the basis of ab initio calculations, and the nature of the Kekule structure is obtained based on, the deviation from this aromaticity. The deviation is calculated by the CiLC method for benzenes annelated to one of three types of small rings, revealing Mills-Nixon and reverse Mills-Nixon effects. The deviation from the aromaticity is determined by the relative dominance of sigma strain-induced bonds or the potential field of adjacent atoms or groups.