KTa_0.63Nb_0.37O₃and Cu doped KTa_0.63Nb_0.37O₃ nanocrystallines were synthesized using a solvothermalmethod at 200°C for 24 h. The obtained samples were characterized by X-ray diffraction, X-ray fluores-cence and scanning electron microscopy, which investigate the influence of Cu-doping on grain size andmicrostructure. Results show that the synthetic nanocrystallines are cubic morphology and well-crystallized. Copper dopant amount is better to be controlled under 1.0 mol% to prevent impurities.KTa_0.63Nb_0.37O₃ nanoparticle size increases and particle dispersity is improved after Cu-doping.