The molecular oxygen-mediated decomposition of the binuclear complex, prepared from oxomolybdate(V) and L-(+)-cysteine, was studied spectrophotometrically at pH 3.5–5.6. The formation of MoVI was detected. The effects of pH and [O2] on the decomposition kinetics are given by the equation: [fórmula] with the apparent first order rate constant, kobs, expressed in s−1 and the concentrations in molar units.