Nanoparticles of the TiO2/ZnO composite photocatalysts were prepared via sol-gel process. The crystalline structure, morphology, thermal stability, and pore structure properties of the composite photocatalysts were characterized by XRD, FE-SEM, TG-DTA, and N2 physical adsorption measurements. The photocatalytic activity of the composite catalysts was evaluated by photocatalytic degradation reaction of methyl orange (MO) in aqueous solution. The best preparation parameters for the composite photocatalysts were obtained through systematical experiments. Furthermore, the photocatalytic degradation reaction of aqueous MO solution followed the first-order reaction kinetics; the relative equation can be described as ln(C0/C)=0.5689t, and the calculated correlation constant (R2) is 0.9937 for the calibration curve.