Abstract: The method of UV-irradiation grafting acrylic acid on the poly-lactic acid (PLLA) film surface was used to improve the hydrophilicity and cell compatibility of polylactic acid. Total reflection infrared spectroscopy, atomic force microscopy and osteoblasts compatibility of the PLLA surfaces before and after modification were investigated. Effects of different treatment conditions on the surface grafting density, surface morphology and surface contact angle were studied. Effects of poly(acrylic acid) grafted on PLLA surface on the osteoblast compatibility were also examined. Results showed that the acrylic acid was successfully grafted onto the surface of PLLA, and the concentration of acrylic acid and grafting time could greatly influence the grafting density. Atomic force microscopy results showed that the surface roughness of acrylic acid grafted PLLA increased significantly. Osteoblast cell culture results showed that acrylic acid grafted PLLA surface could promote the growth of osteoblasts.