Relative permittivities, epsilon(r), and refractive indices, n(D), have been measured for binary liquid mixtures of cyclohexanone (C6H10O) with dichloromethane (CH2Cl2), trichloromethane (CHCl3), 1,2-dichloroethane (CH2ClCH2Cl), trichloroethene (CHClCCl2), and cyclohexane (c-C6H12) at T = 303.15 K. The values of the deviations of epsilon(r) and n(D) from values arising from mole fraction average, which are represented respectively by Delta epsilon(r) and Delta n(D) have been calculated. Values of epsilon(r) and Delta n(D) have been fitted by the method of least squares to smoothing equations, he, for the various mixtures has been discussed from the viewpoint of the existence of specific interactions between the components.