Rhodium phthalocyanin was shown to exhibit high catalytic activity toward oxalic acid oxidation in terms of the onset potential and current density. The onset potential for the oxidation of oxalic acid is much lower than those of the previous electrodes. The substrate specificity and the effect of anion were also examined. The results suggest that oxalic acid would first coordinate to the Rh centerin the catalytic cycle. An amperometric sensor for oxalic acid was constructed using Rh phthalocyanin. This sensor worked at a low applied potential (0.75 V vs. a reversible hydrogen electrode). The limit of detection of the sensor reached 1 mu M. (C) 2009 Elsevier Ltd. All rights reserved.