The effect of Ag nanoparticles on the redox reactions of organosulfur compounds was investigated. Adding the nanoparticles to 2,5-dimercapto-1,3,4-thiadiazole (DMcT)-polyaniline composites, redox activity of the composites was enhanced due to electrocatalytic activation of DMcT by the nanoparticles. It was expected that adsorption of DMcT to the nanoparticles would make a positive contribution to the electrocatalysis.