The PLA/Rice straw fiber composites with various content ratios were prepared by using an internal mixer and a flatten press. The thermal properties, interface effect and mechanical performance of as-prepared PLA/Rice straw fiber composites were studied by mechanical performance measurement, TG, DSC and SEM technique. It was found that increasing the content of rice straw fiber leads to the decrease of the melting temperature while the improvement of the crystallinity of these composites. Introducing the rice straw fibers into PLA matrix does not result in any enhancement of mechanical property. However, the tensile strength of the composite increases as the content of rice straw fiber increases from 10% to 30%. The interface effect between fibers and PLA was obviously observed by SEM photo. It was thought such an issue could be improved by the addition of appropriate coupling agents into the composites.