The chemical and electrochemical behaviour of ions containing chromium in molten NaOH has been investigated as a function of the acidobasicity of the melt. Chromium (VI) dissolved as CrO42- is stable in acidic solution where it is electrochemically reduced successively to CrO43- and to solid NaCrO2. CrO42- is unstable in basic melts and is reduced to CrO43- by O2- after about 3 h yielding stable green solutions. CrO43- is reduced electrochemically to soluble CrO44-. CrO(4)(3- )is also stable in neutral melts and may be oxidized or reduced, respectively, to CrO42- at the anode and to CrO(4)(4- )at the cathode. The results obtained in this work allow us to propose the stability diagram of species containing chromium in molten NaOH at 623 K.