The aim of this study is to investigate the effectiveness of isora fibre mixed with 1% calcium carbonate (CaCO3) as reinforcement for polypropylene (PP) thermoplastic matrix. Isora fibers were subjected to mercerization prior to blending with PP in order to obtain good interfacial adhesion with the matrix. A PP/isora composite has been prepared by melt blending of PP with 5%, 10%, 15%, 20% alkali treated Isora fibre in co-rotating twin screw extruder. The extruded strands are pelletized and then injection moulded to obtain specimens. The optimum compositions of the PP/alkali treated isora composites were mixed with 1% CaCO3. Fibre-matrix adhesion will be analysed by mechanical and thermal properties of the composites were evaluated.