he possibility of protonation of polyaniline (PANI) by functionalized acids such as camphorsulfonic acid (HCSA) is one of the most outstanding reecnt results about this conducting polymer. Here, optical multichannel analysis (OMA) is used to characterize the optical properties of PANI—CSA during its polarization in an electrochemic cell. Compared with PANI doped in usual mineral acid solutions. PANI—CSA displays a remarkable stability during the electrochromic cyclings.