A complex of meso-tetrakis (4-sulphonatophenyl) porphyrin covalently linked to titanium dioxide has been studied. Illumination of the complex with visible light was shown to result in formation of cationic radicals of the porphyrin. Shape and kinetics of the electron spin resonance signals were analysed which permitted calculation of spectroscopic parameters characterising the photoinduced process of the radicals formation. The dye-semiconductor complex was thoroughly characterised to indicate its possible applications.