The formation of a plumbate network in binary lead silicate glasses was examined based on the leaching behavior of Pb2+ in lead silicate glasses over a wide composition region. The effective diffusion coefficient of Pb2+ at 40 degrees C was on the order of 10(-17) m(2)/s for PbO < 35 mol% glasses, and increased three orders of magnitude for 35-50 mol% PbO contents. Such a steep composition dependence is considered to be because of changes in the medium or longer range structure. That is, it is proposed that the plumbate network forms a percolative 3D network in the composition region to form diffusion paths for the lead ions. In addition, the present results indicate that the lead ion exists as a network former over the entire glass forming composition range of the binary silicate glasses.