Electrochemical behaviour of isatin monohydrazone (IM) on a hanging mercury drop electrode in the Britton-Robinson (B-R) buffer solution of pH = 2.00 - 9.00 has been investigated using square-wave voltammetry (SWV) and cyclic voltammetry (CV) techniques. In the pH range of 2.00 - 5.00, the voltammogram of IM exhibited a single cathodic irreversible peak. When the pH value exceeds 5.00, a new cathodic irreversible peak was also seen. According to the voltammetric data, a plausible electrode reaction mechanism of IM was proposed. The first reduction peak of IM is resulted from the reduction of = N-NH-group with consumption of 2e(-)/2H(+). Also, its second cathodic peak is formed by the participation of 2e(-)/2H(+) for the reduction of -N=N-group on its tautomeric form.