Highly sulfonated polyaniline prepared via a synthetic scheme using leucoemeralding base (LEB-SPAN) has been studied using X-ray photoelectron spectroscopy (XPS). A sulfonation level (S/N ratio) as high as 0.80 +/- 0.10 has been revealed in XPS analysis, agreeing well with the element chemical analysis results (similar to 0.78). This contrasts to an S/N ratio of 0.50 for SPAN made via the earlier reported synthetic method. The detailed S 2p and N 1s peak analyses both show that the oxidation level is similar to 50%, implying a better thermal stability of emeraldine oxidation state over those of leucoemeraldine and pernigraniline oxidation states. These XPS analysis results are supported by UV-tis and FT-IR analysis results. The method of resolving 2p 3/2 and 2p 1/2 peaks in the S 2p spectrum is discussed.