Alkali-doped FeV oxide catalysts supported on alpha-alumina were prepared and their catalytic activity in the combustion of diesel soot is reported. The catalysts were characterized by XRD, TPR and SEM-EDX analysis. The influence of the nature of the alkali metal (K and Cs), the temperature of treatment of the catalysts and the stability to sulfur poisoning have been investigated. Catalysts doped with Cs were the most active and stable also after several combustion cycles and in the presence of sulfur in the stream. The activity measurements and microstructural results suggest that the combustion of soot is favored on catalysts where amorphous phases and/or mixed Fe-V-O phases, ensuring an intimate contact between iron and vanadium, are present. A reaction mechanism involving the participation of the redox couple Fe(II)-Fe(III) in the activation of the vanadium combustion sites, is proposed.