The current efficiencies and electrode potentials were determined at 25° C. for the simultaneous electrolytic oxidation of molybdenum to soluble molybdate and to insoluble oxide at current densities between 0.005 and 0.4 amp./sq. cm. in potassium hydroxide solutions ranging between 0.2 N and 5 N. The current density‐electrode potential relation for the formation of molybdate and of oxide is shown by curves. At high current densities and low concentrations of KOH, the oxide product consisted of a mixture of greenish Mo(OH)4 and the colloidal blue Mo3O8. The average valence of the molybdenum in this mixture was 5.3. The two molybdenum compounds could not be satisfactorily separated for analysis. No oxygen evolution was observed. The current efficiency for molybdate formation, which takes place according to the reaction: Mo + 6 F + 8 OH− = MoO4−− + 4 H2O, increases with increasing concentration and decreasing current density (Fig. 2). The curves showing the relation between electrode potentials at given current densities and the concentration of KOH are similar to those found for ferromanganese anodes. On the other hand, no minimum was found in the curves of current efficiency plotted against concentration of electrolyte, as appears for both ferromanganese and ferrochromium anodes. Results indicate that with increase in current density the polarization in the anodic oxidation of molybdenum to molybdate is greater than the polarization in the oxidation to oxide.