Well-defined and perfectly dispersed [(square SiO)Au-1] surface species supported on silica have been obtained via surface organometallic chemistry and transformed upon mild reduction (H-2, 300 degrees C) into small (1.8 +/- 0.6 nm) Au particles supported on silica passivated with SiMe3 functionalities. improved performance in liquid-phase aerobic epoxidation has been achieved, and the intrinsic activity of gold in oxidation is revealed.