Abstract The reactions of tungstophosphate with cobalt ion and the properties of heteropolytungstates containing cobalt have been investigated. Unsaturated heteropolyanion PW11O397− produced by the partial degradation of the parent 12-tungstophosphoric acid reacts with cobalt ion to give 11-tungstocobaltophosphate PCoW11O40H25−. Discussion is given on the presence of cobalt in the heteropolyanion and on the above reaction. Both 12-tungstocobaltate-(II) and -(III) are very resistant to acid, but 11-tungstocobaltophosphates lose cobalt ion in strongly acidic solutions to give the parent 12-acid. Some aspects of the spectra of the heteropolytungstates, in which cobalt(II) and cobalt(III), respectively, are present in the specific site, are discussed.