The one-step synthesis of barium titanate (BaTiO₃) nanoparticles was studied by employing a low-pressure spray pyrolysis (LPSP) method. The effects of temperature, pressure, and the addition of urea to the precursor were investigated experimentally. The results were compared with the experimental data of the conventional (atmospheric) spray pyrolysis method. It was shown that the BaTiO₃ nanoparticles could be synthesized by the low-pressure method, while only spherical hollow particles with smooth surfaces could be produced by the conventional spray method. The addition of urea greatly improved the crystal growth and particle breakup due to extra heat supplied during the combustion reaction coupled with the evolution of gases. The dispersity of nanoparticles increased with the quantity of urea and with a decrease in pressure. The possible mechanism of the formation of BaTiO₃ nanoparticles in the LPSP process was also proposed.