AbstractRice straw (Oryza sativa L.) pulp was treated by high intensity ultrasonication to make fibrils. The rice straw fibril (RSF) material was used as reinforcement in an RSF/polypropylene (PP) composite. The influences of RSF and coupling agent (MAPP) contents on tensile properties of the composite were tested. The results showed that when RSF loading was 5%, the tensile strength rose to a maximum value of 31.7 MPa. With increasing fibril loading the tensile modulus increased first, then decreased. However, the elongation at break decreased with increasing fibril loading. There was no significant influence of MAPP content on tensile strength and elongation at break of PP and RSF/PP composite. When MAPP content was 4%, the tensile modulus of PP and RSF/PP composite all showed maximum values.