Abstract: Bamboo fibers (BF)/polylactic acid (PLA) biodegradable composites are prepared by injection molding process. The natural degradation properties of BF/PLA composites were studied by the methods of X-ray differaction XRD, gel permeation chromatograph(GPC), 3D video microscope and scanning electron microscope(SEM). The results show that, BF is first degraded in natural degradation of composites, and PLA is degraded stratified, resulting in significant mass loss of composites; ester groups in PLA molecule chain react with water, which fractur molecular chain and declined crystallinity, the average molecular weight of PLA is gradually decreased and the molecular weight distribution narrows; the BF/PLA composites become dark with rough surface, partial nudity BF is visible, and tensile and impact strengths of composites reduce. After 12 month degradation, the mass loss rate of BF/PLA composites reachs 8.87%, the average molecular weight of the PLA in composites is reduced by 25.9%, the impact and tensile strengths of composites are reduced by 44.0% and 43.8% respectively. The natural degradation of BF/PLA biodegradable composites in the soil is relatively slow.