An X-ray photoelectron spectroscopic (XPS) study was carried out on the following soluble polyaniline perchlorates and polyaniline base: (A) a perchlorate prepared in a single step by the use of copper(II) perchlorate as an oxidative coupling agent; (B) a polyemeraldine base obtained by treating perchlorate A; and (C) a perchlorate obtained by the protonation of the polyemeraldine base. The N 1s XPS peak of perchlorate C exhibited a more intense envelope on the higher binding energy side than the N 1s peak of perchlorate A. The difference spectrum, with a peak maximum at 402.0 eV, can be assigned to the bipolaron nitrogen in perchlorate C, when referred to the previous spectroscopic study of the two perchlorates. The area of the bipolaron peak was 5% of the whole peak of perchlorate C, although the charged nitrogen was 30% of the total nitrogen. Polarons are the major charge carriers in the two conducting polyaniline perchlorates, and perchlorate C contains bipolarons (in 5% of the total nitrogen) that coexist with polarons.