A nickel hexacyanoferrate modified electrode was constructed by mechanical immobilization. A reversible peak with midpoint potential of 0.38 V was observed in cyclic voltammetry with 0.1 M NaNO3. Electrocatalytic oxidation of thiosulfate was effective on the modified electrode at a significantly reduced overpotential of 0.5 V and at broad pH range. The modified electrode can be used for the determination of thiosulfate in the concentration range of 7.0 × 10–4 to 5.6 × 10–3 M. It has been used for the amperometric determination of thiosulfate in photographic effluents. The results obtained were in good agreement with those obtained by other methods.