Counterion binding has been investigated for poly(allylamine) hydrochloride (PA1AmHCl) in aqueous alcohols (methanol, ethanol, and 2-propanol). The activity of Cl- was estimated as an apparent value by using an ion-specific electrode and compared with the theoretical prediction obtained from a counterion condensation theory. Marked deviations or overestimations of the counterion activity obtained by the theoretical method were observed for the higher-concentration regions of the respective alcohols. This has been attributed to a specific counterion binding which should be more favourable in a medium with a lower dielectric constant and of a lower solvation energy. Similar deviations were also observed for the molar conductivities of the polymer in the same solvent systems. These latter deviations could be remarkably reduced by introducing the extra interaction energy term, i.e., Delta E(ex), for the specific counterion binding that was used to correct the observed deviations for the counterion activities. By utilizing the Delta E(ex) values as a measure of this specific counterion binding, the dependence on the alcohol species has been discussed in terms of the dielectric constant, preferential solvation and the Gutman-Mayer acceptor number.