Abstract: The polypropylene (PP)/sisal cellulose microcrystalline (MCF) composites was prepared by use of rosin sea pine acid grafting poly(12-hydroxy stearic acid) (RA-g-PHS) as a hyper-dispersant, and the effect of hyper-dispersant content on the mechanical properties, melt flow rate and thermal properties of the composites were investigated. Moreover, the impact fracture surface of the composites was observed with scanning electron microscopy. The results indicated that the impact strength and melt flow rate of PP/MCF composites reached 16.8 kJ/m2 and 2.06 g/10 min, respectively, when 2 wt % of RA-g-PHS was incorporated. The composites also achieved optimum thermal properties.