The colorimetric analysis for determining residual thiosulfate in processed photographic materials has been recently investigated instead of the methylene-blue method used as a current standard. In this method, cadmium iodide is used for preparing the blue iodostarch solution, however, it is undesirable to use the reagent in view of the protection of environmental pollution. In this study, an another iodide compound was used instead of CdI₂. The sample of processed photographic paper was immersed in eluent and the effluent was then added to a blue ZnI₂-KIO₃-amylose (iodine-amylose) solution. The amount of residual S₂O₃^2- in sample was measured from the absorbance of the solution at 605 nm. An analytical sensitivity and repeatability in this experiment were discussed. The stability of the iodine-amylose solution for aging and the effect of the presence of developing agent on the measurement of residual S₂O₃^2- were also discussed. The result was obtained that ZnI₂ was fairly used instead of CdI2 for determining the residual S₂O₃^2- by the colorimetric method. ZnI₂-amylose solution also showed the good stability for aging as well as CdI₂-amylose solution. The results obtained from two different methods, colorimetric and methylene-blue, used with a same sample were compared.