Conducting poly(aniline-co-o-anisidine) (PAS) films with different ratios of aniline units in the polymer chain were prepared by oxidative polymerization of different molar ratios of aniline and o-anisidine in 1 M HCl using cyclic voltammetry. Due to the much higher reactivity of o-anisidine, the structure and properties of PASs were found to be dominated by the o-anisidine units. The polymerization of poly-o-anisidine and PASs followed zero-order kinetics with respect to formation of the polymer (film thickness) and the autocatalytic polymerization of aniline was completely inhibited. In contrast to polyaniline, a decrease in the polymerization temperature was found to increase the amount of copolymer formed and its redox charge. The presence of aniline units in PASs led to a pronounced increase in the molecular weight and conductivity, and a decrease in the solubility in organic solvents. Repetitive charging/discharging cycles showed that PASs resist degradation more than polyaniline.