The behavior of uranyl ions in molten potassium polymolybdates at 1073
-1173 K in air is studied by voltammetry and chronopotentiometry. An e
xchange reaction occurs between the electrolysis products, i.e., UO2+/
-x and MoO2-y, in which MoO2 acts as an O-2-acceptor. The conditions a
re found that enable me O/U ratio in UO2+/-x, to be controlled from 1.
981 to 2.105 by electrolysis of polymolybdate melts.