A network-structured SnO(2)/ZnO heterojunction nanocatalyst with high photocatalytic activity was successfully synthesized through a simple two-step solvothermal method. The as-synthesized samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, N(2) physical adsorption, and UV-vis spectroscopy. The results show that the SnO(2)/ZnO sample with a molar ratio of Sn/Zn = 1 is a mesoporous composite material composed of SnO(2) and ZnO. The photocatalytic activity of SnO(2)/ZnO heterojunction nanocatalysts for the degradation of methyl orange is much higher than those of solvothermally synthesized SnO(2) and ZnO samples, which can be attributed to the SnO(2)-ZnO heterojunction, the pore structure, and higher Brunauer-Emmett-Teller (BET) surface area of the sample: (1) The SnO(2)-ZnO heterojunction improves the separation of photogenerated electron-hole pairs due to the potential energy differences between SnO(2) and ZnO, thus enhancing the photocatalytic activity. (2) The SnO(2)/ZnO sample might possess more surface reaction sites and adsorb and transport more dye molecules due to the higher BET surface area and many pore channels, also leading to higher photocatalytic activity.