In this investigation, we studied the preparation of organic-inorganic hybrid films consisting of BSA and calcium phosphate (CaP). Different types of thin film were prepared at different BSA concentrations. The responses of osteoblastic human osteosarcoma (HOS) cells to the hybrid films were analyzed using scanning electron microscopy (SEM) and attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR). SEM observations demonstrated that the concentrations of BSA used affected the variation of the surface morphology of the films. As the BSA concentration increased, the surface porosity of the film increased. However, at 1 mg/mL of BSA, the maximum BSA concentration used in this study, thin film formation was retarded significantly, which may indicate that the presence of BSA tends to restrict the formation of thin films. Insitu ATR FT-IR spectra were obtained for the films with variation of the incubation time. The peaks at 1750∼1380 cm-1 representing amide bonds indicated the presence of BSA within the film. The peaks in the 900∼1200 cm-1 region attributable to the phosphate group in calcium phosphate and the peak at 1110 cm-1 representing the P-O band of low-crystallinity hydroxyapatite clearly demonstrate the presence of BSA within the calcium phosphate film. Analyses of the adhesion, proliferation, and differentiation assays of HOS cells on the hybrid films were executed to examine the biocompatibility and osteointegration of the films. The adhesion of the HOS cells increased upon increasing the BSA concentration. However, at the maximum concentration used in this study, 1 mg/mL, the HOS cells adhered less than the other films. The proliferation of HOS cells decreased upon increasing the BSA concentration. In contrast, the differentiation of HOS cells increased upon increasing the BSA concentration. Therefore, the decrease in the proliferation of HOS cells on the films prepared at higher BSA concentrations can be attributed to the improved activity of the differentiation of HOS cells. These results clearly demonstrate that the hybrid films prepared in this study possess excellent biocompatibility and osteoconductivity.