The effects of ZnO additive on the phase formation, microstructure and electrical conduction of Y-doped BaSnO3 have been investigated. The single-phase and dense BaSn0.75Y0.25O3−δ compound with 4 mol% ZnO additive was successfully prepared after sintering at 1300 °C, which significantly reduces the sintering temperature. The conductivities measured under dry and wet air atmospheres reveal that the bulk conductivity of BaSn0.71Y0.25Zn0.04O3−δ is much lower than that of BaSn0.75Y0.25O3−δ. However, ZnO as a sintering aid does not affect the bulk conductivity. The total conductivity of BaSn0.75Y0.25O3−δ with ZnO as the sintering aid is slightly higher than that of unmodified BaSn0.75Y0.25O3−δ, and reaches 2.4 × 10−3 S cm−1 at 621 °C. Therefore, this material can be used as a proton-conducting electrolyte for intermediate temperature solid oxide fuel cells.