Rare earth elements can improve the performance of polymers because of their special 4f orbitals. The nucleation and stabilization of radical groups of rare earth particles can affect the structure of polypropylene (PP) and its properties. In this study, samarium oxide (Sm2O3) particles were used as a cocatalyst and nucleating agent in polypropylene-graft-cardanol (CAPP) grafted by reactive extrusion. The properties of polypropylene-graft-cardanol containing modified Sm2O3 with a titanate coupling agent (CAPPMS) were investigated by ultraviolet–visible spectrometry, polarizing microscopy, differential scanning calorimetry, scanning electron microscopy, universal testing, and capillary rheometry with the reference of CAPP containing unmodified Sm2O3 particles. The results show that the titanate coupling agent (TCA-401) coated on the surface of the Sm2O3 particles improved the dispersion of the Sm2O3 particles and the adhesion between the Sm2O3 particles and CAPP matrix. The Sm2O3 particles promoted more cardanol to graft onto PP. Acting as nucleator for CAPP, the Sm2O3 particles increased the crystallization rate, increased the melting temperature, and decreased the spherulite size of CAPP. The modified Sm2O3 particles showed a greater effect on the mechanical and rheological properties than the unmodified Sm2O3 particles did. The tensile strength, impact strength and flexural strength of CAPPMS increased by 10 MPa, 0.64 kJ/m2, and 6.5 MPa, respectively, compared to those of CAPP when we used 4.5 mol % modified Sm2O3 particles. The viscosity of CAPPMS increased to a certain extent in the presence of the modified Sm2O3. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41012.