Electrocatalytic reduction of L-cystine (CySSCy) was examined on glassy carbon electrodes coated with the title conductive polymer in which Pt, Pd, Cu, Ag, and Hg thiolates were fixed. Pt and/or Pd thiolate fixed in the polymer behaved as excellent electrocatalytic active sites for reductive cleavage of the sulfur sulfur bond in CySSCy.