Abstract: Polypropylene(PP)/sisal fiber(SF) composites were prepared by using maleic anhydride-grafted polypropylene(PP-g-MAH) as an interfacial modifier, and the effect of fiber content on the flowability, combustion performance, and thermal and mechanical properties of the composites were investigated. The results indicated that the melt flow rates of the composites were reduced by 3.1 g/10 min with the addition of 30 wt % SF, but their Vicat softening points increased by 5.1 ℃, compared with pure PP. Moreover, their tensile strength and bending strength increased by 6.0 MPa and 20.7 MPa, respectively. In addition, there is a decrease in impact strength by 3.1 kJ/m2 for notched specimens and by 60 kJ/m2 for the unnotched ones.