Rice straw (Oryza sativa L.) pulp was treated by high intensity homogenizer to make fibril and fibril aggregates. The rice straw fibril and fibril aggregates (RSFs) material was used as reinforcement in a RSFs/ Poly (vinyl alcohol) (PVA) nanocomposite that prepared by film casting. The diameter distribution of RSFs was investigated by laser diameter instrument (LDI) and its crystallinity was evaluated by wide angle X-ray diffraction (WAXD). The morphological of RSFs was investigated by scanning electron microscopy (SEM). The mechanical properties were measured by tensile test and the dynamic mechanics analysis (DMA), thermal stability tests, i.e., differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) and the Fourier transform infrared spectroscopy (FTIR) test were also performed, respectively.