Based on energy saving, environmental protection and use of agricultural residues, rice straw/starch composites were manufactured using molding method. The influence of manufacturing parameters (time, pressure and temperature) on flexural strength, flexural elastic modulus and tensile strength of the composites had been studied. The microstructure of fractured surfaces was further observed. Results showed that when the manufacturing parameters are: time of 47min, pressure of 19MPa and temperature of 156°C, the composites have higher mechanical properties. The mechanical properties increase with increasing of pressure. The interface, soakage and compatibility of cassava starch and straw are better, starch content is 16%, and straw/cassava starch composites have higher mechanical properties.