The mechanism of electropolishing of titanium in methanol-sulfuric acid electrolytes is studied by steady-state measurements and by ac-impedance spectroscopy using a rotating disk electrode. The effect of applied potential, electrode rotation rate, temperature, and electrolyte composition on the response of the system is investigated at the mass-transport-limited current plateau. Both steady-state measurements and impedance data suggest that the rate of reaction is controlled by mass transport of tetravalent titanium species from the anode surface to the bulk electrolyte. The impedance data confirm the presence of a compact film at the anode surface during titanium dissolution at the limiting current.