This study implemented an electrochemical analysis method, square-wave voltammetry, to monitor the molten fluoride (LiF-NaF) baths which are used for electrolytic deposition of niobium. This method makes it possible to perform qualitative and quantitative analyses of the niobium species in situ at different degrees of oxidation and to determine the content of oxygenated niobium compounds. Square-wave voltammetry was first compared with the cyclic voltammetric technique and then its applicability area was defined in terms of frequency range. Using the standard addition method, the calibration straight lines were constructed giving the specie＇s reduction peak differential current densities leading to the metallic deposition of niobium and of the niobium＇s oxyfluorinated compound according to their respective concentrations and the disproportionation constant for Nb-IV into Nb-V and Nb was estimated for a temperature of 780 degrees C. Finally, an overall mass balance was performed on the niobium to verify the coherence of the results obtained in this study on the system in equilibrium.