In vivo surface properties of the metallic biomaterials used for artificial joints, bone plates, dental implants, etc. are discussed on the basis of empirical data, focusing on the destruction, regeneration, and reconstruction of the surface oxide film in body fluids. Metal ion release from metallic materials occurs through the remaining surface oxide film and with its destruction. The released metal ions are active and immediately combine with water molecules or anions to form oxides, hydroxides, or inorganic salts. Thus, the ions have only a small chance for combination with biomolecules to cause toxicity. Other types of ions can survive in body fluid in an ionic state and eventually combines with biomolecules and cause toxicity. The surface modification techniques for biomaterials to improve corrosion and wear resistance and also for hard tissue compatibility are reviewed. Effect of calcium ion implantation into titanium for improvement of its hard tissue compatibility is given as an example.