In this paper, in situ Fourier Transform Infrared Spectroscopy (FTIRS) is used to study the electro-catalytic oxidation mechanism of shikimic acid (SA) at a copper electrode in H(2)O and D(2)O solution, respectively. As the potential is applied between 0.1 V and 0.2V vs. SCE, SA is oxidized to 3-dehydroshikimic acid (DHS). Then a significant change appeared when the potential is scanned from 0.3 V to 0.8 V, DHS is decomposed to transaconitate and formate. As the potential is over 0.9 V, formate is further oxidized to CO(2). Density functional theory (OFT) calculation of the IR spectra is in good agreement with the experimental observation. The adsorption of transaconitate through carboxyl on copper electrode is also evidenced by p- and s-polarized radiation in FTIRS. (C) 2011 Elsevier Ltd. All rights reserved.