Polymer compounds including both antimony and molybdenum were formed by mixing freshly prepared solutions of antimonic and molybdic acid. These acids were formed through an ion exchange process. When antimony is in excess, molybdenum is included in the high polymers having the ccp structure of β antimonic acid. When molybdic acid is in excess in the starting mixture, molybdenum-rich polymers with a larger molecular weight than molybdic acid were formed. In GPC experiments the behaviour of the compounds is related to their Mo and Sb content. The elution volume is only related to the molecular weight of the compound when Sb is the main component and imposes its structure.Keywords: molybdoantimonic acids, inorganic polymers, ultracentrifugation, GPC.