Physical and optical properties of xPbO-(100-x) B2O3 (x=20-50 mol %) lead-borate glasses were investigated. The density of these glass samples increases from 4.267 to 5.960 g/cm3 whereas the molar volume decreases initially and then increases continuously as the content of PbO increases. PbO's dual role (modifier and glass former) in the glassy matrix is responsible for the non-uniform variation in density and the uneven pattern in molar volume. The UV-visible spectra also revealed a non-uniform variation in optical band gap with increasing PbO content, confirming that PbO enters the glass network as a modifier at low concentrations and as a glass former at high concentrations. Other parameters, such as average boron-boron separation and oxygen packing density (OPD) decrease progressively as PbO content increases, while the refractive index, the molar volume of oxygen (V0) and packing density (Vt) increase linearly. Because of the presence of lead, the ionic behaviour of the prepared glasses increases while covalency decreases, indicating that these can be used to make solid state ionic devices.