Abstract: The process of collagen adsorbed on poly-lactic acid (PLA) surface was systematically studied by quartz crystal microbalance (QCM).The effects of ionic strength and pH were investigated. The results indicate that the adsorption amount of collagen firstly increases and then decreases with the increasing ionic strength. The ionic strength has different impact on the adsorption amount of collagen from various sources. The adsorption amount varies with pH; pH for the peak adsorption amount is slightly smaller than that at the isoelectric point. Atomic force microscopy images show that the structures of adsorption collagen layer from various sources are completely different.