The homogeneous oxidation of oxalate has been investigated at an ultramicroelectrode by means of redox catalysis with different iron and ruthenium coordination complexes. Kinetically, the process is governed by the first electron transfer. It can be rationalized by Marcus theory. When the electron acceptor is a ruthenium coordination complex, the second electron transfer can generate a luminescent excited state of the ruthenium. This electrochemiluminescent process is related, in a first approximation, to the catalytic efficiency of the homogeneous oxalate oxidation, but also to the different competing routes for the second electron transfer (oxidation of CO2.-). The effect of the pH and the ionic strength on the redox catalysis and the light emission are discussed.