The dielectric constants and excess dielectric constants in non-polar + polar binary liquid mixtures of toluene with alkanols (methyl alcohol, ethyl alcohol, propyl alcohol and isopropyl alcohol) have been studied at 303, 313 and 323 K temperatures and over the complete mole fraction range. The dielectric constants for these mixtures were measured using a microcontroller based system. The results are negative over the entire range of composition. Symmetrical curves were observed for the systems in which the minimum occurs approximately at 0.5-mole fraction of toluene. The results are discussed in terms of intermolecular interactions. In order to predict the dielectric data for non-polar + polar binary liquid mixtures, five mixing rules were applied and the results indicate that the predictions of the five mixing rules are satisfactory. The investigation of dielectric constant of mixed solvents bearing alcohols aims at better comprehension of their biological, chemical, pharmaceutical, technological and laboratory applications. (C) 2013 Elsevier B.V. All rights reserved.