It was shown previously that (i) if the surface of a biomaterial is covered with TiO2 (tetragonal structure oxide), it shows a high initial contact angle and a high change rate in contact angle (i.e. a higher spreading process); while (ii) cubic structure oxides show relatively lower spreading rates in 1% NaCl solution at 25°C. Shot-peening has been applied to biomaterials (especially titanium and its alloys) to improve their fatigue strength. It is well known that shot-peening causes surface roughening. The effects of surface roughness on wettability are not well documented. Therefore, in the present study, the effects of shot peening on the initial contact angle and changes in it as a function of time, were investigated. In addition, the spontaneous half-cell potential of all tested biomaterials were measured to correlate the wettability phenomenon to initial surface chemistry. Pure titanium and its alloys, including Ti-6AI-4V and NiTi alloys, AISI Type 316L stainless, Co-Cr alloy, and pure nickel, were mechanically polished, shot-peened and pre-oxidized at 300°C for 30 min in pure oxygen. It was found that (i) shot-peening homogenized the surface conditions in terms of initial contact angles, (ii) TiO2 oxide shows a higher spreading coefficient, while cubic structure oxides show a lower value, and (iii) the spreading coefficient was correlated to the magnitude of the spontaneous half-cell potential.