To improve the toughness of PLA, Poly(lactic acid) (PLA)/organically modified montmorillonite (OMMT) nanocomposites were prepared via a masterbatching method. Melt index test indicated that nanocomposites had a better processability compared with pure PLA. When the loading of MMT was 3 wt%, the nanocomposites showed the maximum tensile strength (63.81MPa), and its elongation at break increased by 2.6 times compared with pure PLA. The thermal properties and crystallization behaviors of pure PLA and nanocomposites were studied by Differential Scanning Calorimeter (DSC). With OMMT loaded, the crystallinity of PLA in nanocomposites increased from 7.34% to 16.66%. The microstructure and morphology were studied by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). It revealed that the average grain size reduced compared with pure PLA, and most of layer structure of OMMT was exfoliated.