Carbon-doped anatase with spherical shape of aggregates has been synthesized by the developed precursor technique with the use of Ti(OCH2CH2)(2) as a precursor. The synthesized samples of the general composition TiO2-y C (y) :nC with different carbon content have been tested for the photocatalytic activity in the oxidation reaction of water-dissolved hydroquinone during irradiation in ultraviolet and visible light. It was shown that the optical and photocatalytic properties of TiO2-y C (y) :nC depend strongly on the concentration of carbon. The first-principles calculations of the electronic band structure and optical absorption spectra have been carried out. The probabilities of formation of carbon for oxygen substitutional defects and interstitial defects (implantation of carbon atoms into interstitial sites) have been analyzed. The calculations performed allowed us to determine the dominating type of defects responsible for absorption and photocatalytic activity of carbon-doped anatase in the visible spectral region. [GRAPHICS] .