In photooxidation tests of nicotinamide adenine dinucleotide (NADH) in titanium dioxide slurry containing Ag+. Cu2+, Ni2+, Fe3+, [Fe (CN) (6)](3-) or Fe(III) -EDTA as an electron acceptor, the oxidation rate of NADH was the highest when Fe(III)-EDTA was included in the slurry. In the range of initial concentrations of Fe(III)-EDTA of 0-100 x 10(-3) mol/m(3), it was found that the oxidation rate of NADH increased with an increase in Fe(III) -EDTA concentration during the early phase of photoreaction, and thereafter the reaction system reached a pseudo-steady state with elapsed time, giving an approximately constant oxidation rate of NADH.