The invention relates to the use of sulphonic, phosphonic and phosphoric acids functionalized with plasticizing groups as dopants for conductive polyaniline films and for conductive polyaniline-based composite materials. These acids correspond to the following formula (I): ##STR00001## in which: R.sub.1 represents --SO.sub.2(OH) or --PO(OH).sub.2 or --OPO(OH).sub.2; the R.sub.2 groups, which are identical or different, represent a hydrocarbonaceous group, such as a 2-ethylhexyl, butoxyethyl or isopropylbenzyl group; R.sub.3 and R.sub.4 independently represent a direct bond or a hydrocarbonaceous group, such as a methylene group.