[en] A photometric method for the evaluation of stepwise and overall formation constants of molybdylhydroxo-aminobenzenethiolate chelate has been described. The characterization of the complex has been done on the basis of analysis, thermogravimetric analysis, magnetic susceptibility measurements and IR spectra. The formation of MoO(OH)³⁺ species is explained via protonation of MoO₂(ABT)₂ chelate species as supported by IR spectral studies. The presence of inter- and intra-molecular hydrogen bond in the chelate is indicated by a lowering in νO-H and νN-H frequencies. The stepwise formation constants (log k₁ < log k₂ < log k₃) and overall stability constant (log K or log β₃) are found to be 1.79, 2.82, 3.80 and 8.35 at 25 +- 1 deg C, respectively. The free-energy chan.o.e for the reaction (log K = 8.35) is -11.2 kcal mol^-1. (author)