Effect of replacement of Pb 3O 4 by CuO on structure and properties of pseudo-binary [75%] Li 2B 4O 7–[25 − x%] Pb 3O 4 glass system, where x = 0, 5, 10, 15, 20 and 25 mol% CuO, have been investigated. IR spectra of the prepared glasses show that CuO goes into the network and play also a role as a glass modifier. The addition of CuO decreases the formation of tetrahedral groups (BO 4) and increasing the triangle one (BO 3), led to increase the borate non-bridging oxygen (NBO). The observed increase in T g with CuO reflect increase in bond strength, also the glass-forming ability and stability decrease with increasing CuO reflects the reduction of the network rigidity and loosening of glassy structure. The density and molar volume were discussed in terms of the structural modifications that take place in glass matrix. The distance between Cu and Cu atoms and the polaron radius have been carried for all samples.