Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BZT–0.5BCT) thin films were prepared from two ceramics targets, Ba(Zr_0.2Ti_0.8)O₃ and (Ba_0.7Ca_0.3)TiO₃, using dual-magnetron sputtering, and a LaNiO₃ (LNO) seed layer was introduced between the film and Pt(111)/Ti/SiO₂/Si substrates via a sol–gel technique. Domain structures were observed on the thin films by piezoelectric force microscopy (PFM), and then an autocorrelation function technique was applied to analyze the obtained PFM images. The mean sizes of the domains of the BZT–0.5BCT and (001)-oriented BZT–0.5BCT/LNO thin films are 69.2 nm and 151 nm at room temperature respectively. On the basis of our results, it is proven that the nanodomains have a large effect on the piezoelectricity of the thin films for MPB composition: the converse piezoelectric coefficient d₃₃ is 258 pm V⁻¹ for BZT–0.5BCT thin films and 122 pm V⁻¹ for BZT–0.5BCT/LNO thin films. It is worth noting that not only the crystal orientation, but also the domain structures play critical roles in the piezoelectricity for the BZT–0.5BCT thin films. Furthermore, (001)-oriented BZT–0.5BCT/LNO thin films exhibit excellent dielectric properties and the dielectric constant (ε ∼ 1046) is dramatically increased compared with the BZT–0.5BCT thin films (ε ∼ 168). The C–V results indicate that both of the thin films are ferroelectric in nature.