A range of coloured electronic or mixed ionic-electronic glasses has been evidenced in the Na 2 O-MoO 3 -P 2 O 5 system. The properties of these glasses have been studied along different composition lines corresponding either to a fixed Na 2 O content or a constant Mo/P ratio. An EPR spectroscopy investigation of these glasses has allowed to determine the Mo 5 + ion percentages in these materials. The electrical properties of these glasses have been studied by impedance spectroscopy, and the electronic and ionic contributions have been evaluated. The properties of these sodium glasses have been compared with those of lithium glasses with the same compositions.