In the seventies, Professor Theodore Kuwana used thin-layer spectroe lectrochemical technique to study the electron transfer of cytochrome oxidases. Since then, many scientists take the advantage to work on metalloporphyrin redox reactions . By applying suitable potential to metalloporphyrin systems and by taking the spectra at the same time, either the oxidized or reduced species can be identified. This characterization is essential for the mimicking the biosystems by metalloporphyrins. Some examples have been selected to illustrate the application of spectroe lectrochemistry on metalloporphyrins.