Germanate-tellurite glasses with the molar compositions of x GeO2-(70-x) TeO2-5K2O-5Na2O-10Nb2O5-10ZnO-0.2Er2O3 (x=0,10, 25, 50, 70) have been investigated for developing 1.5μm fiber and planar amplifiers. Effects of GeO2 on the thermal stability and optical properties of Er3+-doped germanate-tellurite glasses have been discussed. It is noted that the thermal stability of the glasses are improved and the maximum phonon energy are increased by increasing GeO2. Adding GeO2 increases the Judd-Ofelt parameters Ω2, Ω6 but decreases the stimulated emission cross sections σe. According to the McCumber theory, the maximum peak of σe is 9.92×10-21cm2 at 1.53μm in germanate-tellurite glasses. The maximum FWHM of Er3+4I13/2→4I15/2 emission spectrum is 52 nm. In addition, the intensity of upconversion luminescence of the Er3+-doped germanate-tellurite glasses decreases rapidly with increasing GeO2 content.