In this report, a novel method for the synthesis of polyaniline in aqueous medium, based on a G-quadruplex DNAzyme-catalyzed oxidation and polymerization of aniline by hydrogen peroxide in the presence of a polyanionic template, is described. The synthesis is simple and the experimental conditions are mild. The polymerization of aniline is carried out in an acidic aqueous medium with a catalytic amount of the DNAzyme. It was found that aniline polymerization occurs in a pH range from 2.0 to 5.0 with an optimal pH of 3.0. The polymerization kinetics can be described by the classical Michaelis–Menten reaction mechanism. Comparing to the horseradish peroxidase-catalyzed polymerization of aniline, the advantages of using the DNAzyme as the catalyst in the polymerization of aniline are cost-effectiveness and greater tolerance to the acidity of the reaction solution and high concentrations of hydrogen peroxide.