The composite of ZnO-Co2O3, were prepared by thermal wet mixing method. This research consists of two parts, the first preparation of coupled (ZnO-Co2O3 by normal wet treatment mixing then calcinating in a furnace (900ºC) for 3 hrs. The mixing semiconductor products were studied by using X-ray diffraction, and FTIR analysis. The second part of this work includes the study of photcatalytic degradation of n-undecane using prepared coupled (ZnO-Co2O3), which is achieved by the irradiation of suspended solution consists of different concentration of n-undecane with coupled (ZnO–Co2O3) by using solar source/mercury lamp (125 Watts). In order to study the effect of mixed metal oxide (ZnO-Co2O3) in photcatalytic degradation of n-undecane, several experiments were carried out in various conditions to attain the best photcatalytic degradation of n-undecane. These experiments include the effect of mass catalyst, light inrtensity, substrate concentrations and the effect of temperature. The products were analysis by using gas chromatography technique.