Abstract: To improve the degradability of poly (L-lactic acid) (PLLA) and prepare the bone repair material with good mechanical properties, the composites consisting of PLLA and MgO nanoparticles (MgO-NPs) have been prepared. The result suggests that, compared with pure PLLA, modified MgO nanoparticles (g-MgO-NPs) significantly enhance its dispersion in PLLA matrix and its interfacial bonding with PLLA matrix. With addition of 4%(mass ratio) g-MgO-NPs, the tensile strength of film increases from 10.6 MPa to 30.1 MPa, and its elongation at break decreases from 71% to 59%. The pH of film tends to be a relatively stable value and be close to that of the physiological saline after degradation. It reveals that g-MgO-NPs improve the degradability and mechanical properties of polylactic acid composite films in a certain extent.