Abstract: Wood flour was modified in sequence by toluene-2,4-diisocyanate(TDI) and stearic acid(SA), and then the modified wood flour were mixed with polypropylene(PP) in a twin screw extruder to produce PP/wood flour composites. The influences of the molar ratios of SA and TDI on the surface properties of wood flour, mechanical and processing properties of the composites were studied. The results show that the surface tension of the modified wood flour decreases step by step generally, and the interfacial tension between the wood flour and PP decreases at first and then increases with the raise of molar ratio of SA and TDI. Mechanical tests reveal that, compared with the unmodified composites, SA and TDI have no obvious influence on the tensile, flexural and notched impact strength, but the unnotched impact strength of all modified composites is improved. When the molar ratio of SA and TDI is 1.07, the unnotched impact strength and melt-mass flow rate of composites reach 9.74 kJ/m2 and 13.12 g/10 min, respectively, improving by 77% and 22% compared with unmodified composites.