Heat-treated cobalt tetramethoxyphenylporphyrin (CoTMPP) on carbon support (Black Pearls) is well known as a highly active material for the electroreduction of oxygen in acidic electrolytes. However, in the process of catalyst formation at high temperatures aggregation of the carbon-supported particles occurs, causing a detrimental decrease of the active surface. This contribution describes for the first time an alternative preparation method for a CoTMPP-based electrocatalyst via low-temperature plasma treatment suppressing particle aggregation. Different parameters of plasma (duration of treatment, power, gas composition) have been varied in order to investigate their influence on the preparation process. After treatment, the electrochemical activity of the samples has been tested by rotating-disk-electrode technique and cyclovoltammetry. Their structural features were characterized by UV-visible and infrared-spectroscopy. A comparison of the results with argon plasma-treated carbon-supported CoTMPP catalyst reveals higher electrochemical activity as with the heat-treated sample. The investigations open up new preparation strategies using the special features of plasma technology for surface-optimized catalytic materials. (c) 2005 The Electrochemical Society.