A series of carbon/polyaniline (C/Pani) composites were synthesized by oxidative polymerization of aniline in the presence of carbon in acid media. Biomass-derived activated carbon (AC) having 1740 m2/g surface area was used as the carbon component. The aniline loadings varied from 8 to 60 wt%. A composition of the composites was determined by CHNS analysis. Porous structure of polyaniline, carbon and C/Pani composites was characterized with nitrogen adsorption at 77 K. Structure of the composites, polyaniline and carbon was studied by Fourier transform infrared spectroscopy (FTIR). Electrochemical properties of the samples were investigated by cyclic voltammetry technique in 1 M H2SO4 at 25 °C. It has been shown that the aniline loading and presence of the carbon in the reaction mixture determine final product of the polymerization. At the aniline loading <30 wt%, 4-aminodiphenilamine (4-ADPA) and phenazine-ring containing structures (PhzR) being intermediates in the aniline polymerization are predominantly formed and registered by electrochemical methods. Polyaniline formation is observed for the samples with aniline loading >40 wt%.