This work was aimed to investigate the effect of alkalization treatment on the fiber-matrix interfacial interaction and hence their compatibility. Kenaf fiber was treated using a 6% NaOH solution for 8 hours. The composites were produced by mixing the treated fiber with PP at various temperatures, duration, and fiber composition. Alteration on the surface chemistry of the fiber was identified by performing FTIR analysis. The surface energy of the treated fiber was mathematically derived from the contact angle measurement results. The compatibility level between treated fiber and PP matrix was visualized through FESEM analysis. Tensile strength tests were also conducted to obtain data necessary for exploring the relationship between the thermodynamic aspects of the fiber-matrix interfacial interaction and the mechanical properties of the composites. The FTIR spectra show that there was significant increase in the %transmittance at wavelength range of 3100-3600 cm-1 indicating that O-H groups were degraded during treatment. However, the polar component of the surface energy for treated fiber was instead higher compared to the untreated one. The SEM images show that there are no noticeable reduction in the size of the treated fibers as expected. On the other hand, the tensile strength of the PP-treated fibers composites reached its highest value when the matrix were loaded with fibers at the lowest percentage i.e. 5%.