A convenient one-step solvothermal route has been developed to synthesize monodispersed barium titanate with narrow size distributions. The key point of this method is the controlling of hydrolysis of Ti(OC4H9)(4) with Diethylene glycol. The as-prepared BaTiO3 nanoparticles were characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, BET-specific surface area measurement and Raman spectrum. The monodispersed BaTiO3 nanoparticles obtained by this method have an average size of 5 nm with a narrow size distribution and a lattice tetragonality of 1.0069 +/- 0.0010, which is promising for the ferroelectric science and its industry application.