The rate of H 2 evolution from aqueous suspensions of Pt/TiO 2 with deposited zinc porphyrin in the presence of an electron donor (EDTA, triethanolamine, ascorbic and oxalic acids) during irradiation by visible light ( λ > 520 nm) was optimized with respect to the concentrations of platinum, zinc porphyrin and electron donor. The relationship between the rate of hydrogen evolution and pH has a maximum at pH 4–5 for EDTA, ascorbic and oxalic acids, as does the adsorption of these donors on TiO 2. In the case of triethanolamine, H 2 production increases sharply in alkaline solutions when the triethanolamine molecules are deprotonated. The photostability of the photosensitizer increases on the semiconductor. Turn-over numbers for the zinc porphyrins varied from 50 for water-soluble zinc porphyrin up to 150–185 for water-insoluble sensitizers.