The enhancement of the photocatalytic activity of TiO2 was investigated as a function of added amount of other oxides to promote desired oxidation or reduction reactions. Mixed oxides of Nb2O5 or Li2O with TiO2 were prepared by the sol-gel process. The target material of dichloroacetic acid (DCA) was chosen for oxidation reactions and K2Cr2O7 for reduction. While the Nb2O5/TiO2 had a deleterious effect on the decomposition rate of DCA, the excess electrons due to the doping of Nb2O5 into TiO2 promoted the reduction process for Cr6+. Li2O (1 wt%) with TiO2 was found the most efficient photocatalyst for DCA oxidation, resulting in photocatalytic activity of 50%.