Because of its extreme hardness, diamond is a very interesting material for many industrial applications. One way to extend the field of diamond application and optimize the process conditions in diamond tool production is to enhance its surface reactivity. Low-pressure oxygen-plasma treatments were applied to equip the diamond surfaces with chemically reactive groups to improve their adhesion properties. XPS and DRIFT spectroscopy investigations showed that oxygen plasmas were suitable to oxidize the diamond surface. Combining derivatization reactions and solvatochromic dye adsorption studies, the introduction of alcoholic groups was confirmed. Besides the surface oxidation, the plasma treatment initiates decomposition of the diamond lattice which is followed by a re-arrangement of the carbon atoms in a graphite-like structure. The planar graphite structure supports the formation of carbonyl groups.