X-ray diffraction patterns from two different nematic samples viz (i) 1-hexyl-4-(4-isothiocyanatophenyl) bicyclo, [2,2,2] octane and (ii) 4'-(pentyloxy)-4-biphenyl carbonitrile, were recorded using Laue type of arrangement, consisting of flat 2D-image plate detector. Using these recorded data and employing three different models orientational order parameter[1] < P-2> and the higher order parameter < P-4>, have been computed and analyzed. The order parameters estimated from X-ray method is also compared with that obtained from optical method.