In this study, vetiver grass fiber was used as a natural filler in natural rubber (NR) and polylactic acid (PLA) composite. Glycidyl methacrylate grafted natural rubber (NR-g-GMA) was used as a compatibilizer. The main objective of this research is to study the degradability of PLA and PLA composites under soil burial test. It was shown that vetiver grass fiber showed a significant role in the degradability of PLA composites under soil burial condition. Mechanical properties of PLA composites dramatically decreased after burial in soil compared to those of pure PLA. Moreover, addition of vetiver grass fiber at 20 and 30% (w/w) content led to a significant increase in weight loss of the specimens with increasing burial time. From SEM micrographs, better interfacial adhesion between PLA, vetiver grass fiber, and NR particles was observed with the addition of NR-g-GMA. This indicated that the compatibility of PLA/vetiver/NR can be improved by using NR-g-GMA. Furthermore, mechanical properties of injection molded PLA and PLA composites were compared with those of compression molded samples. Injection molded specimens of neat PLA and PLA composites showed higher tensile strength than compression molded specimens. This may be due to the result of higher fiber orientation along flow direction in injection molding.