The rice straw fiber (RSF) was modified by suspension polymerization of butyl acrylate (BA) monomer. The results of Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) indicated that poly(butyl acrylate) (PBA) was adsorbed and coated on RSF. The biodegradable composites were prepared with the modified rice straw fiber (MRSF) and poly(lactic acid) (PLA) by HAAKE rheometer. Mechanical properties showed that the tensile strength of PLA/MRSF composites (W(%) = 7.98) increased by 6 MPa compared with blank sample. The water absorption of the PLA/MRSF composites was lower than PLA/RSF composites. The thermal properties of these composites were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA results confirmed that thermal stability of PLA/RSF composites increased with the PBA increasing. The DSC data showed that RSF played a role as a nucleating agent and PHA made crystallization of PLA more difficult and incomplete. (C) 2010 Elsevier B.V. All rights reserved.