Various protonated poly(o-anisidine) (PoAN)/poly(vinyl alcohol) (PVA) composites were prepared with different types of acids: sulfuric (SA), p-toluene sulfonic (TSA), camphor sulfonic (CSA), and p-dodecylbenzene sulfonic (DBSA). In the visible spectrum of each composite in dimethyl sulfoxide, three absorption peaks were observed at 440, 620, and 860 nm. The peaks at 440 and 860 nm, which were enhanced with the increasing content of acid-doped PoAN in the PVA matrix, were attributed to the radical cation and localized polaron generated in the conducting polymer. However, the peak at 620 nm was ascribed to the emeraldine base (EB) form of PoAN; that is, a portion of the acid was detached from the conducting polymer to form EB-PoAN and free acid. The linear dependence of the logarithmic electrical conductivity on the variation of humidity, which was observed for all the composites, was caused by the salt-base transition of the conducting polymer, that is, by the movement of free acid between the active sites of the conducting polymer and the strongly bound water existing in PVA, which in turn depended directly on the environmental humidity. The response time of the composites to humidity was shortened with a decrease in the size of the dopant anions: DBSA > CSA > TSA > SA.