The conditions for strontium titanate (SrTiO3, ST) nucleation and particle growth were investigated for preparation of ST/ barium titanate (BaTiO3, BT) complex nanoparticles. The conditions with and without ST nucleation were clarified. Epitaxial growth of ST layer on the BT substrate particles was studied using both conditions. Unfortunately, the ST/BT complex nanoparticles with heteroepitaxial interface were not prepared, but a new two-step solvothermal reaction method was developed. Finally, the ST/BT complex nanoparticles without heteroepitaxial interface were successfully prepared.