Ce0.5Zr0.5O2 (CZ) plays an important role in three-way catalyst for its outstanding oxygen storage capacity (OSC). However, CZ decomposes into Ce- and Zr-rich phases after high-temperature calcinations, which results in the degradation of OSC. In this study, CZ was synthesized using a coprecipitation method. Subsequently, different amounts of Ba2+ ions were introduced into the CZ using an incipient wetness impregnation method followed by calcination at 1000°C for 2 h to obtain a series of so-called BCZa powders. The Ba2+ ion addition effects on the phase development, specific surface area, crystallite size, agglomeration, and OSC of CZ were investigated. The addition of 0.5–3 wt% Ba2+ ions significantly increased the specific surface area and inhibited CZ phase separation. However, with the addition of Ba2+ ions at or above 10 wt%, severe agglomeration occurred and Ba(CexZr1−x)O3 (0<x<1) was detected, both of which contributed to lowering the OSC of BCZa. With the addition of 5 wt% Ba2+ ions, the BCZa exhibited the maximum OSC (91.4 μmol/g), due to the high abundance of active oxygen species on the interface between Ce0.5Zr0.5O2 and BaZrO3.