Ba(Zr0.2Ti0.8)O3 (BZT) thin films were deposited on Pt/Ti/LaAlO3 (001) substrates by radio-frequency magnetron sputtering at different O2/Ar mixing ratios. As the O2/Ar ratio increased (1/4–4), the preferred orientation evolved from (00l) to (111). The grain size and the surface roughness increased, and the ferroelectric properties improved with increasing O2/Ar ratio. The BZT thin films deposited under oxygen-rich atmosphere (O2/Ar = 4) had larger dielectric constant (443) and tunability (44%), while the BZT films deposited under argon-rich atmosphere (O2/Ar = 1/4) had a lower loss tangent (0.016).