Impedance of Mo electrode is measured in the Mo-oxide melt system to determine the kinetic characteristics of processes which occur at the boundary of Mo with the Mo-ion containing oxide melt. Electric conductivity of the latter is determined as well as a dependence of Mo electrode potential on oxide melt basicity. The equimolar melt of Na, B and Si oxides with the additives of MoO3 is used in measurements. Relation of diffusion coefficients of Mo(VI) and Mo(II) ions in the above melt with 0.5-3.0 % MoO3 at 700 and 800°C is evaluated.