Abstract: Studies are made on graphitised carbon fibres using wide-angle X-ray diffraction technique and Scanning/Transmission Electron Microscopy (SEM/TEM) to obtain structural parameters and morphological features of the fibres. Two important crystallite size structural parameters La and Lc can be generally obtained from X-ray diffraction technique. Lc values are evaluated by applying the necessary correction factors for the non-separation of Kα1 and Kα2 doublet and instrumental broadening. For simplicity empirical expressions are developed for these correction factors from the standard monograms. The surface features of pitch and PAN graphitised carbon fibres at high resolution are examined using SEM and orientation studies are made using TEM. Finally crystallite domain size parameters are related to the tensile modulus of the fibres. It is found that the crystallite domain size increases with the graphitisation temperature and stretching loads. This in turn leads to the enhancement in the tensile modulus of the fibre.