Oscillatory bending responses of a solid polymer electrolyte membrane (SPM)-platinum (Pt) composite synchronized with anodic potential oscillations under galvanostatic conditions were determined. The oscillations took place when the anodic oxidations of formaldehyde or sodium formate in aqueous :sulfuric acid solutions were carried out on a plated Pt electrode. The frequency and the waveform of the: oscillations depended on the concentration of the organic compounds and the direct current applied. The phenomena are discussed in the light of a previously published model in which we proposed that the interfacial stress between the membrane and the electrolyte causes the bending response.