By irradiation with a low pressure mercury lamp, photolys is of oxalato-titanium(N) complex was studied in aqueous solution at constant pH with excess amount of oxalic acid to prevent any secondary reactions, such as hydrolysis of the primary product.In the presence of excess amount of oxalic acid, the composition of oxalato-titanium(N) and ()complexes were investigated spectrophotometrically and were assumed t be TiO(C20i)2 2 and Ti(C20k)2Irradiation of a solution of oxalato-titanium(N) complex in excess amount of oxalic acid, in which the molar ratio of Ti(N) and oxalic acid is 1: 10, led to photoreduction and hydrolysis of the complex. The photoreduction reaction forms an oxalato-titanium()complex with evolution of carbon dioxide. The hydrolysis reaction gives a precipitate of titanium(N) hydroxide with evolution of carbon dioxide and carbon monoxide.Furthermore, a photosensitized reaction of oxalic acid by the oxalato-titanium()complex oceured during the irradiation. Consequently, oxalic acid decomposed to carbon dioxide and earbon monoxide.The initial reduction rate and the final reduction ratio decreased linearly with increase of pH value of the sample solution. Thus, it was found that H ion contributed to the photoreduction of oxalato-titanium(N) complex.