The comparative analysis of the physicochemical properties of polyaniline prepared in the conditions of solventless mechanochemical treatment in the ball mill (PAni|mch) and polyaniline synthesized by the usual oxidative polymerization in the solvent (PAni|c) is carried out. Conductivity of PAni|mch substantially exceeds that of PAni|c. As molecular weights of PAni|mch and PAni|c are comparable, the observed difference could be connected with the influence of mechanical stress which affects the polymer during its mechanochemical preparation. The increased conductivity of polyaniline obtained by post-synthesis mechanochemical treatment of PAni|c (PAni|mt) confirms such explanation. It could be concluded from the results of the structural investigations as well as of spectral and electrochemical studies that the shear stress which exerts influence on the polymer during mechanochemical synthesis or mechanochemical treatment leads to the increase of the interchain π–π interaction and, consequently, to the efficient improvement of conductivity.