Abstract: Cellulose nanocrystals(CNC) modified by rosin were used to synthesize rosin grafted cellulose nanocrystals(R-CNC). And R-CNC was applied as filler to strengthen natural rubber(NR) forming rosin grafted cellulose nanocrystals reinforced natural rubber composites(R-CNC/NR). FT-IR, UV-Vis, scanning electron microscope(SEM), X-ray diffraction(XRD) and tensile strength were employed to investigate the properties and performance. The successful grafting of rosin from CNC could be proved by FT-IR.The grafting rate of rosin calculated by UV-Vis was 30%. XRD proved that R-CNC/NR had excellent crystallinity. SEMtest showed that R-CNC had better compatibility with NR. Tensile test showed that the tensile strength of NR was 0.33 MPa. When the content of CNC was 40%, the tensile strength of natural rubber reinforced by cellulose nanocrystals(CNC/NR) was 1.56 MPa and the elastic recovery value was 88.75%. When the content of R-CNC was 40%, the tensile strength of R-CNC/NR was 2.87 MPa and the elastic recovery value was 90.04%. Therefore, the reinforcing effect of R-CNC on NR was better than that of CNC.