The thermal stability and spectroscopic properties of Er3+-doped Na2O-GeO2-PbO glasses were investigated experimentally. The thermal analysis results show that the thermal stability of the investigated glasses is improved with replacing GeO2 by PbO. Subsequently, Judd-Ofelt (J-O) approach was applied to the room temperature absorption of Er3+ (4f(11)) transitions to determine J-O intensity parameters. The reduced values of Omega(2) with the substitution of PbO for GeO2 indicate the decrease of covalency of Er-O bonding. The stimulated emission cross section of the (4/)13/2 --> (4/)15/2 transition increases as a consequence of the increase of refractive index of glass hosts and the narrowing of fluorescence bandwidth with the increase of PbO. The abnormal large emission cross section and large bandwidth in the Na2O-0.8GeO(2)-0.1PbO glass arises from the change of germanium coordination with oxygen. (C) 2004 Kluwer Academic Publishers.