0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) epitaxial thin films were grown on SrRuO3 (SRO) coated (001)-oriented SrTiO3 (STO) single crystal substrates by pulsed laser deposition under different oxygen partial pressures in the processing of deposition. The effects of oxygen partial pressure on structure, cation stoichiometry, surface morphology, leakage current behavior, ferroelectric, and piezoelectric properties were investigated. Both the lattice parameters and (Ba+Ca)/(Ti+Zr) cation ratio decrease with increasing oxygen partial pressure. The BCZT thin film with the ideal cation stoichiometry was obtained under 200mTorr, giving rise to a remanent polarization P-r=14.5C/cm(2) and effective piezoelectric coefficient d(33)=96 +/- 5pm/V.