The optical properties, birefringence and order parameter of two alkoxycyanobiphenyls (nOCBs, where n = 5 or 8) have been studied as a function of temperature. The variation of orientational order parameter has been determined experimentally. Theoretical order parameter values have also been computed in the smectic range using McMillan potential and in the nematic range using Maier-Saupe potential and compared with the experimentally obtained values. The variations of polarizabilities with temperature have also been evaluated from density variation and birefringence studies.