There is provided a fluorine-containing polymer having an ionic group which has a heteroaromatic ring and is useful as a material comprising various heteroaromatic ring compounds having a stable fluorine-containing heteroaromatic ring, and further a fluorine-containing polymer having a heteroaromatic ring which is useful as a starting material of the above-mentioned polymer or a curing agent. Also, there is provided a fluorine-containing polymer having a heteroaromatic ring such as imidazole in its side chain, a polymer salt thereof, and a polymer composition comprising such a polymer and a polymer salt and a nano filler.