Glasses of the system (ZnO)x−(P2O5)1−x have been prepared by melting ZnO with anhydrous P2O5 in open crucibles. These glasses had compositions ranging from 20 to 70 mol % ZnO (chemically analysed ZnO mol %). Measurements of the thermal conductivity for the present glass system have been made in the temperature range 305 to 630 K. The thermal conductivity of this glass system is mainly due to lattice thermal vibrations. The thermal conductivity data are found to be fairly sensitive to the ZnO mol % content. It is observed from these data that the present glass system can be divided into three compositional regions. This behaviour is qualitatively explained in terms of changes in glass structure.