The electroreduction of PbSO4 film formed on Pb in 4.5 mol.dm^-^3 H2SO4 at -0.6V (vs. Hg/Hg2SO4/4.5mol.dm^-^3H2SO4) for 20 min has been studied using linear sweep voltammetry, chronoamperometry, in conjunction with AC impedance method. The experimental results show that most of the film can be electroreduced. At early stage, the electroreduction takes place at the surface of the lead sulfate grains in the film, conforming to an instaneous nucleation and three-dimensional growth mechanism under diffusion control. Then Pb^2^+ is electrodeposited on the lead layer formed previously, which is limited by the radial diffusion of Pb^2^+ out of the grains. The liquid films among the particles in the grains may be the major passages for ion transportation.

Key words: SULFURIC ACID, LEAD, ELECTRODE REACTION, LEAD SULFATE, ELECTROLYSIS OF CHLORIDE