The purposes of this research were to study the effects of solution pH on the photoelectrochemical properties of TiO 2 photoelectrode and the adsorption behaviors and photocatalytic reactions of two dyestuffs (Reactive Red 22, RR22 and Basic Red 2, BR2) in aqueous solution using various photocatalyst films (TiO 2 and Nafion-coated TiO 2 , Nf/TiO 2 ). The open circuit voltage and the short circuit photocurrent of TiO 2 photoelectrode increased as solution pH decreased and indicated more photoelectrons were generated in acidic solutions. The response times reaching half maximum photovoltage and photocurrent were determined to be faster in acidic solutions than those in alkaline solutions, indicating higher electron diffusion occurred in acidic solutions. The coating of 0.5g of Nafion per gram of TiO 2 was enough to reduce the zeta potential of Nf/TiO 2 to less than −20mV in aqueous solution and exhibited a hydrophobic surface that might decrease the adsorption and photocatalytic decomposition of dye. Experimental results on the adsorption and photocatalytic decomposition of RR22 and BR2 indicating that the charges of TiO 2 surface and reactant dye markedly influence the reaction rate. The photocatalytic decompositions of RR22 using TiO 2 were favored to occur in acidic conditions and exhibited a minimum decomposition rate near the isoelectric point of TiO 2 . Nevertheless, no obvious RR22 decompositions were found in experiments conducted using Nf/TiO 2 . Decompositions of BR2 using both TiO 2 and Nf/TiO 2 were more favorable in alkaline conditions; however, decompositions of BR2 were found to be decreased in experiments conducted using Nf/TiO 2 .