Objective;The purpose of this study was to investigate the effects of chondroitin sulfate-A (CS-A) on culture of osteoblasts in vitro.Methods: Various concentrations of CS-A were added to the cultures of human osteoblasts, and the cell proliferation quantity, calcium content and alkaline phosphatase activity of cell layers were evaluated. Results: The CS-A in low concentrations (1 mg/ml and 0.5 mg/ml) promoted the proliferation of osteoblast, while in high concentration(10 mg/ml )inhibited the proliferation of osteoblast slightly. The CS-A prevented calcium accumulation in the cell layers, although CS-A had no inhibition on alkaline phosphatase activity. Condusion: The CS-A can affect proliferation and mineralization of osteoblast, but has no effect on differentiation of osteoblasts.