In this article, the influence of a rare-earth (RE) coupling agent on the interfacial interaction of wood flour/polypropylene composites (WF/PP) was investigated by studying the rheology behavior and the mechanical properties and using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The increased equilibrium torque results implied that the composites had a greater frictional shear force, which probably resulted from strong adhesion at the interface between the WF and PP. The mechanical property results showed that the added RE improved: the tensile strength by 42.6%; the flexural strength by 66.7%; and the impact strength by 92.3%, when compared to the WF/PP composites containing no RE material. According to the DSC results, the addition of the RE decreased the crystallization temperature and melting temperature. These results showed that the RE improved the interfacial adhesion. This was further confirmed by the SEM analysis of the composites. (C) Koninklijke Brill NV, Leiden, 2012