The effects of antimony on the formation process of 3PbO . PbSO4.H2O (3BS) on Pb and Pb-Sb electrodes have been studied by linear sweep voltammetry (LSV), etc. Experimental results indicate that the formation of 3BS depends on the behavior of the PbSO4 passivation layer. When the anodic film is passivated seriously, the diffusion of ions through the PbSO4 layer is the rate-determining step in the formation of 3BS. As the passivation layer is partly re-activated, the rate of 3BS formation is controlled by solid state nucleation and growth under the diffusion limitation. In the positive potential sweep, the presence of Sb in the alloy promotes the formation of 3BS, and the amount of 3BS formed becomes greater with decreasing H2SO4 concentration.