Combined ultrahigh vacuum electrochemistry is applied to study the effect of sulfur on copper oxidation in aqueous solution. Chronoamperametric studies show that pulsing a Cu electrode modified with similar to 0.1 monolayer of adsorbed S results in an approximately 50 s plateau in the current-time profile after a slight initial decay in current. Following the plateau period, the current-time profile is observed to exhibit a final phase of current decay. In contrast, a S-free copper electrode exhibits immediate current decay. X-ray photoelectron spectroscopy analysis reveals that Cu2O is the main oxide growing on both S-free and S-modified copper surfaces under these conditions. On the S-free copper surface, oxide covers the surface almost immediately after the pulse. On the S-modified copper surface, oxide growth continues for similar to 70 s after the pulse. The data indicates that the final phase of current decay on the S-modified Cu surface occurs only when oxide growth is essentially complete. Oxide growth is significantly retarded by the presence of sulfur.