The orientational order parameter is one of the most important material parameters of nematic phase. In the present work, the phase transition temperatures of the mesogenic mixtures are measured by using a polarizing optical microscope. The birefringence in nematic phase is estimated by measuring ordinary and extraordinary refractive indices. The birefringence is also measured by measuring the diameter of Newton’s rings at various temperatures in nematic phase. The orientational order parameter is evaluated by using the birefringence data obtained in the above two methods. The orientation order parameter can be enhanced by the dispersion of different nanoparticles in the liquid crystal matrix.