The dielectric behaviour of polar liquids such as propan-1-ol, propionaldehyde and their equimolar binary mixture in non-polar solvent benzene is studied in the microwave frequency range using the cavity perturbation technique at 6.218 GHz (J band), 9.880 GHz (X band), 16.331 GHz (P band) and 24.951 GHz (K band). Ab initio geometry optimization is performed in the 6-31G (d) basis set using the Gaussian 94W program for both pure and binary systems of propan-1-ol and propionaldehyde. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi's method and compared with the ab initio results. Conformational analysis of the formation of hydrogen bond between the propan-1-ol and propionaldehyde is supported by the FT-IR spectra. The average relaxation times are calculated from their respective Cole-Cole plots.