In this study, we investigated the transient catalytic function of SPS in Cu electrodeposition via cyclic voltammetry. The addition of SPS into the electrolyte for Cu electrodeposition caused the shift of the peak potential for the electrochemical Cu2+ reduction in the positive direction. Its catalytic effect was manifested exclusively on Cu electrode and became stronger as Cu electrode was incubated longer in the electrolyte prior to the measurement, which is interpreted to indicate that the catalytic function was associated with the interaction between SPS and Cu+ generated from Cu electrode surface via comproportionation. The change in the concentration of SPS and Cu2+, or the change in the potential of Cu electrode affected the catalytic function, which gives an evidence of the interaction. Cyclic voltammetry on ultramicroelectrode clearly showed the Cu+ generation and the interaction between SPS and Cu+. (C) 2016 The Electrochemical Society. All rights reserved.