Molecular dynamics simulations were performed to investigate the adsorption mechanism of arg-gly-asp (RGD) tripeptide on pit and perfect rutile TiO2 (110) surfaces in aqueous solution and the competitive mechanism of RGD and water. It is shown that the adsorption of RGD on pit surface is more stable than that on perfect surface, and the adsorption energy of the pit surface is -106.14 kcal mol(-1), which is 1.8 times as big as that of the perfect surface. Water influences significantly RGD adsorption on the surface. The water molecules reach first the surface and occupy the adsorption sites, i.e., the water oxygen atoms bond to the surface fivefold titanium atoms to form the stable first hydration layer and interact with the surface bridging oxygen atoms to form the second hydration layer. The subsequent arrival RGD edges out the adsorbed water molecules bonding to the surface oxygen atoms and forms hydrogen bonds with these oxygen atoms. Electrostatic and van der Waals interactions are the main interactions between RGD and hydrophilic TiO2 surfaces.