The redox active properties of CoAPO-5 and CoAPO-44 molecular sieves have been investigated by temperature-programmed reduction, oxidation and desorption. Furthermore, the acidities of the 'reduced' and 'oxidized' forms of the samples were compared by means of temperature-programmed desorption of ammonia and FTIR spectroscopy using pyridine as probe molecule. Additionally, the reactions of 'oxidized' samples with gaseous cyclohexanol or 2-propanol were studied by a pulse technique. All these studies were aiming at a critical reinvestigation of the nature of the redox active sites of CoAPO-n materials and at a quantitative determination of the oxidizable/reducible cobalt species. Neither evidence for a valence state change of an essential portion of framework cobalt ions nor for a significant adsorption of oxygen on such sites were obtained. Therefore, the well known colour changes during oxidative or reductive treatment of CoAPO-n does not necessarily indicate redox processes of the framework cobalt as suggested by many researchers. Rather, the observed redox processes could be attributed to reactions of hydrogen, oxygen and alcohols with non-framework cobalt species.