To enhance the piezoelectric responses, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics were fabricated by a sol-gel method in various sintering atmospheres. The effects of oxygen partial pressure on the microstructure and electrical properties of BCZT ceramics were systematically investigated. The samples sintered in air, O-2 and N-2 are the coexistence of the orthorhombic (O)-tetragonal (T) phase at room temperature. The phase transition temperature of the O-T phase of BCZT samples sintered in air, O-2 and N-2 is gradually closer to room temperature. The results of EDS, XPS and the activation energy confirm the significant effect of oxygen sintering atmosphere. BCZT samples sintered in oxygen atmosphere show excellent ferroelectricity (2P(r) = 31.62 mu C/cm(2), 2E(C) = 3.46 kV/cm) and significantly enhanced piezoelectricity (d(33) = 604.3 pC/N, d33* = 647.5 pm/V and k(p) = 58%), resulting from the minimum oxygen vacancy, the phase transition temperature of O-T closer to room temperature and dense microstructure. These results demonstrate that adjusting oxygen partial pressure in sintering is an effective way to enhance the piezoelectric responses of BCZT ceramics.