A systematic investigation of the electrosynthesis of polyaniline (PANI) films in the presence of various anions has been carried out. These anions were HSO4-, Cl- and ClO4-. The synthesis was followed by doping with SiMo12O404- (SiMo12), which has been proven previously to give very stable and catalytically useful PANI/SiMo12 composites. Another interest of this system is that two of the redox systems of SiMo12 appear in the potential domain where PANI is conductive, and a third one is just at the limit where PANI becomes fully reduced. The study is conducted essentially using the EQCM technique. It is shown that the same amount of doping heteropolyanion is fixed in the film, through an essentially volume process, in open circuit conditions, or by cycling the electrode potential during the incorporation. However, this last technique seems more beneficial to obtain a faster homogeneous dispersion of the dopant anion into the polymer matrix. The results also demonstrate that films preformed in sulfate media are doped very easily with SiMo12, while the plasticization of the films prepared in perchlorate media severely limits this incorporation, whatever the anion (HSO4-, Cl- and ClO4-) present in the incorporation medium. Another important result, revealed by EQCM studies, concerns the charge transport properties of the composite PANI/SiMo12 during its redox processes. It appears, in that case, that proton exchange can constitute the dominant pathway even in a mildly acid medium like 0.5 M H2SO4. More generally, it can be concluded that not only might the nature of the anions in the film compensating the positive sites affect the apparent dissociation constant of PANI, but the redox chemistry of the anions also affects the charge transport processes.