The effects of WO3 addition and sintering condition on the microstructure and electrical conductivity of SrTiO3 ceramics have been investigated. When P-O2 less than or equal to 10(-10) atm, the room temperature electrical conductivity was proportional logarithmically to WO3 content. Whereas when P-O2 > 10(-10) atm, the electrical conductivity increased with WO3 content up to 1.2 mol%. When the WO3 content is higher than 1.2 mol%, the electrical conductivity decreased. The decrease of conductivity seemed to be due to the formation of Sr vacancies. Sr vacancies are considered to be formed by the movement of Sr ions into the grain boundaries. In 3.0 mol% WO3-doped specimens, Sr-W-rich phases have been observed by SEM and EDAX analysis.