12-heteropolyacids (HPA) constitute a large group of compounds with a characteristic anion structure and general formula H8-nX+nM12O40, where X equals P, As, Ge, Si and M equals W, Mo, V. These compounds are widely applied as catalysts, behave as strong acids, and some of them exhibit significant redox properties as well. Recently it has been discovered that HPA can act as a dopant, i.e., convert conjugated polymer chains from their neutral state to the oxidized (polyacetylene, polypyrrole) or protonated (polyaniline) state. Such doping reaction involves simultaneous insertion of heteropolyanions between the chains of polymers possessing an extended (pi) bonding system. The resulting compounds exhibit very interesting catalytic properties. In this paper, FT-IR spectroscopy has been applied to characterize heteropolyanions inserted into conjugated polymer matrices.