The work aims to test and research the properties of polylactic acid/OMMT nanocomposites. Polylactic acid (PLA)/organic montmorillonite (OMMT) nanocomposites were prepared by solution intercalation method, and then the thermal stability, rheological and mechanical properties of such nanocomposites were tested and analyzed. The degrees of crystallinity of PLA, PLA/OMMT (mass fraction: 3%) and PLA/OMMT (mass fraction: 6%) were 13.01%, 15.43% and 18.26%, respectively. The thermal decompositions temperature of PLA, PLA/OMMT (mass fraction: 3%) and PLA/OMMT (mass fraction: 6%) were 336.36, 343.55 and 345.14 ℃, respectively. The residual mass fractions at 336.36 ℃ were respectively 82.45%, 85.57% and 87.58%. The storage modulus and loss modulus were increased with the increase in the frequency when the temperature reached certain value. The loss modulus was greater than the storage modulus within the testing frequency range. Several materials exhibited shear thinning effect, and the viscosity of the composites with more organic montmorillonite nano-content was also significantly enhanced with the increase in the frequency. With the increase in the OMMT content, the tensile modulus was increased, the tensile strength was basically not affected, and the elongation increased first and then decreased. Compared with polylactic acid, the thermal stability of nanocomposites is enhanced, the crystallinity is increased, and the rheological and tensile mechanical properties are improved.