Single-crystalline barium zirconate titanate nanocubes (BZ_xT NCs; x is Zr contents) with various composition of Zr/Ti ratio were synthesized by hydrothermal method using water-soluble titanium and zirconium complex and surfactants. The highly-ordered assemblies of the BZT NCs were directly fabricated on the substrate by dip-coating method with low withdrawal rate. High dielectric constant above 4200 and relative low loss tangent below 1% with extremely small frequency dependence were achieved in the case of BZ_0.2T NC assembly. The temperature dependence of capacitance of BZ_0.1T NC assembly was quite small from −60 to 150°C. A specific peak in the Raman spectra of BZ_0.2T NC assembly was slightly shifted to lower wavenumbers from 294 to 288 cm⁻¹ after heat-treatment which meant the change of local bonding condition was induced by local strains at the interfaces. Zr-substitution and local strain synergistically affected to the dielectric properties of BZT NC assemblies.