The catalytic properties of supported cobalt phthalocyanines, containing different substitutes, in oxidation of ethylmercaptan to disulphide, have been studied in a flow system. The inclusion of electron-donor substitutes in the phthalocyanine molecule leads to an increased catalytic activity, while electron-acceptor substitutes decrease it. In the absence of NaOH the productivity of the most active catalyst samples is unstable and drops quicker than that of the less active ones. In the presence of NaOH the activity of the phthalocyanines is stable and high. This fact is explained and interpreted in terms of the mechanism of the oxidation process.