The reaction of polyaniline with new high-molecular-weight protonating agents, namely poly(alkylene phosphates), has been studied by UV/vis spectroscopy. The spectra were recorded both in the solid state and in organic solvents since polyemeraldine protonated with poly(alkylene phosphates) can be stabilized in the solution without precipitation. The influence of the molar ratio of both polymers and of the length of alkylene chain on the protonation level was observed. The protonation was evidenced by the appearance of polaron bands at 420 and ca. 900 nm. The addition of polar solvent increased the degree of,protonation. The best protonation was achieved in in-cresol solution, whose principal features were the appearance of intrachain (free carrier) excitation at 430 nm, the decrease of the ca. 800 nm band intensity, and the increase of a long absorption tail into the near-infrared.