The phases, microstructure, and electrical and photoelectrochemical properties of the TiO2-ZnO system were investigated as a function of processing variables such as ZnO content and heat treatment condition. in the specimens containing >1 wt% ZnO, the rutile TiO2 and Zn2TiO4 phases were observed. When the sintered specimens were heat-treated in reducing atmosphere, the content of Zn2TiO4 phase decreased and the surface became apparently porous. These results were related to zinc evaporation. Electrical resistivity was influenced by the formation of defects and the Zn2TiO4 phase, rather than microstructural characteristics such as grain size and density. A high photocurrent density of 2.2 mA/cm(2) at 0 V (vs. SCE) was observed for 30 wt% ZnO added to TiO2, resulting from an increase in electrical conductivity and surface reactivity.