Abstract: Lactic acid oligomer was prepared by direct condensation method and used as modifier of nano-calcium carbonate (CaCO₃) to developed modified nano-calcium carbonate (g-CaCO₃). g-CaCO₃ was blended with polylactic acid (PLA) by solution blending to prepare g-CaCO₃/PLA composites. The g-CaCO₃ was characterized by FTIR and oil absorption value etc. SEM, DSC, universal testing machine, rheometer, water vapor transmission tester and UV-Vis-AIR spectrophotometer were used to study the g-CaCO₃ on the structure and performances of the PLA. The results show that the modification of lactic acid oligomer reduces the absorption value of CaCO₃, promotes compatibility between CaCO₃ and PLA and improves the dispersion of CaCO₃ in PLA matrix. At the same time, the g-CaCO₃ acts as nucleating agent in PLA matrix, improving the crystallization ability of the PLA. The tensile strength and strain at break of the g-CaCO₃/PLA composites first rise and then fall as the g-CaCO₃ content increasing. When the g-CaCO₃ content is 5wt%, the tensile strength is 50% higher than that of 5%CaCO₃/PLA composite. When the addition amount of g-CaCO₃ reaches 10wt%, the tensile strength is still 13% higher than that of pure PLA. The storage modulus and complex viscosity of the composites are improved by adding g-CaCO_3. In addition, the addition of g-CaCO₃ enhances the barrier property of PLA to ultraviolet visible light and water vapor.