The effects of multiwalled carbon nanotubes (MWCNTs) modified by silane coupling agent (Trademark in china was KH570) and lactide (LA) on the properties of poly(lactic acid) (PLA) composites were investigated in this paper. The Scanning electronic microscopy (SEM) images showed that MWCNTs modified by both KH570 and LA, which constructed the MWCNTs-KH570-PLA nanocapsules, owned the best performances to toughen PLA. These nanocapsules were developed by solid multilayered interfaces and efficiently enhanced tnced the interfacial adhesion between PLA and MWCNTs. Polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis further verified that modified MWCNTs refined the PLA grain size and improved its crystallization. Moreover, observed by thermogravimetry (TG), the thermal stability of PLA was also improved. Then it could be drawn the conclusion that among these modified MWCNTs, MWCNTs-KH570-PLA nanocapsule was the best in toughening PLA, and the tensile strength of MWCNTs-KH570PLA/ PLA composite rose by 39.97% and its impact strength by 51.61%.