The effect of ZnO on the crystal structure, sintering behavior, and electrical conductivity of yttrium-doped BaCeO3-BaZrO3 was investigated by unfixing or fixing the yttrium content noted as BaCe0.5Zr0.3Y0.2-xZnxO2.9-0.5x and BaCe0.5Zr0.3Y0.2O2.9+yZnO, respectively. Studies on the two series revealed that BaO center dot ZnO eutectic, rather than ZnO, was responsible for the sintering densification. For BaCe0.5Zr0.3Y0.2-xZnxO2.9-0.5x, the evaporation of ZnO center dot BaO eutectic was observed after sintering at 1300 degrees C for 10 h, and few impurities were detected by XRD with x < 0.20. For BaCe0.5Zr0.3Y0.2O2.9+yZnO, the concomitant loss of BaO with ZnO caused A-site deficiency and led to impurities of Y2O3 for y=0.08 and 0.14, and Y2BaZnO5 for y=0.20 during the sintering. For both series, ZnO enhanced the relative density, which was above 97% with x or y varying from 0.02 to 0.08. Energy-dispersive X-ray spectroscopy analysis revealed that ZnO hardly entered the perovskite phase. The conductivity study also suggested that ZnO did not serve as a dopant and that yttrium content was essential for sustaining a high ionic conduction. Excessive ZnO was especially detrimental to the grain boundary conduction and thus lowered the total electrical conduction. The optimized composition of BaCe0.5Zr0.3Y0.2O2.9+0.04ZnO has been obtained, with both a high relative density (similar to 98.5%) and a high electrical conductivity (1.35 x 10-2 S/cm at 600 degrees C).