The variation of Kerr constant in polar-polar binary liquid mixtures, all belonging to aprotic - aprotic in nature are reported for various molar fractions. We found that there is an excess value of Kerr constant with a maximum reaching at a particular molar fraction in the aliphatic-aromatic complexes with the components belonging to different homologous series. This fact has been supported by a similar trend observed in the variation of Kerr effect correlation factor and the excess refractive index at the same molar fraction. The details of the results are discussed. © 1994.