The effect of saccharides, such as glucose, on the photocatalytic decolorization of various dyes has been investigated using TiO2 as a photocatalyst in an aqueous solution saturated with nitrogen. An azo dye, such as Orangell, used as a typical dye, was reduced by cleavage of the azo linkage, as evidenced by the production of sulfanilic acid, All of the dyes tested were decomposed with first-order kinetics. The rate constants of decolorization in the aqueous solution saturated with nitrogen increased with the addition of a saccharide such as glucose. Furthermore, the effect of the reductive saccharides on the photocatalytic decolorization of dyes was quantitatively correlated with their dispersion force, The reaction rate of the photocatalytic decolorization of dyes in the aqueous solution saturated with nitrogen, including glucose, is 7 times that in the solution saturated with oxygen.