We report the values of electro optic Kerr constant of liquids belonging to Carbonyl (Ketone and Aldehyde) and Nitrile series at λ = 632.8nm. These investigations have been carried out for the first time in the liquids, Methyl n propyl ketone, Methyl isopropyl ketone, Methyl isobutyl ketone, Propionaldehyde, Butyraldehyde, Propionitrile and Butyronitrile belonging to these homologous series. We have observed a decreasing trend in Kerr constant values with an increasing chain length by a CH2 intervening group in all these series. The variations in the inductive effect arising from different substituents in the molecular structures of the liquids are used to interpret the decreasing trend in the values of the Kerr constant.