Radial distribution analysis of X-ray intensities diffracted by natural coir fibre subjected to various thermal and mercerization treatments has been carried out. Interatomic distances, mean square displacements and interatomic coupling constants have been obtained from the radial distribution curves. As coir fibre finds its various applications in its natural form, its study has been carried out without disturbing the configuration of its cellulose-lignin complex during the treatments. Interatomic distances remain more or less the same during thermal and chemical treatments but the coupling constants and the mean square displacements experience changes, reflecting the changed mechanical behaviour of the fibre.