In this study, several types of modified methods were tried for improving natural fiber reinforced composites and also three kind of natural fibers were used for reinforced composite. Plasma polymerization increased fiber tensile and composites mechanical properties. It is higher effect than alkali treatment. Resin impregnation was expected cheaper method than plasma polymerization. Polyvinyl Alcohol resin impregnation method can increase fiber tensile strength, interfacial shear strength between fiber and composites mechanical properties. And with Bamboo/polypropylene/maleic anhydride polypropylene water absorption ratio also can decrease. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University