In vitro degradation properties and cytocompatibility of surface-grafted magnesia whiskers/poly(l-lactide) (g-MgO-Ws/PLLA) composite films which obtained by solution casting method were studied in this work. In vitro degradation experiments of the samples were carried out in a PBS solution at 37 A degrees C with a pH of 7.4. Changes in weight, pH value, crystallization and melting behaviors, surface morphology and chemical composition, and tensile property of the g-MgO-Ws/PLLA composite films with the degradation time were characterized, from which the related degradation mechanism of the composite was concluded. Results showed that the weight loss of the g-MgO-Ws/PLLA composite films was slightly higher than that of the neat PLLA. The alkaline g-MgO-Ws can neutralize the acidity of degradation products of PLLA to some extent and maintain the tensile properties of the films well in the early degradation stage compared with neat PLLA. With the degradation, the crystallinity of PLLA matrix increased first and then decreased. In vitro cell culture results, based on the optical density value, alkaline phosphate (ALP) activity measurement, field emission scanning electron microscope, and confocal laser scanning microscopy observation, revealed that the g-MgO-Ws/PLLA composite films were not only in favor of cells adhesion, spreading, and proliferation, but also can significantly upregulate the ALP activity and promote the osteogenic differentiation of MC3T3-E1 cells compared with the neat PLLA film.