The seed coats of jack beans (Canavalia ensiformis) were pulverized and modified via mercerization process. The chemical properties, morphology, Fourier-Transform InfraRed spectroscopy (FTIR) spectra and X-ray patterns of the unmodified and modified samples were studied. The unmodified sample was more acidic and hydrophilic than the mercerized sample. The iodine absorption number of the unmodified sample was 1.98 ml while the mercerized was 1.00 ml. The micrographs of unmodified sample showed irregular shapes of the granules while those of the mercerized derivative were mixes of cylindrical and rod-like shapes, which appeared more crystalline and fibrous than the unmodified. The mercerized sample showed (O-H) spectra of normal polymeric hydroxyl group, which had a characteristic signal of lignocellulosics. In addition, absorption band 2129.24 cm-1, indicating –C≡C– terminal alkynes (mono substituted), was found in the mercerized sample. Very strong N–O of nitro group was observed at 1540.26 cm-1, which disappeared upon modification. The XRD profile showed peaks of both the modified and unmodified as mixes of A- and B- polymorphs, that is, C-type, with high proportion of silicone. The X-ray patterns were unchanged after modification. However, the crystallite size of the unmodified sample increased from 8.60 to 10.10. Therefore, the mercerized fiber were more applicable in the fabrication of fiber-polymer composites than the unmodified fiber.