Abstract: Bismuth tungsten oxide (Bi₂WO₆) powders were synthesized by citrate sol process using ammonium tungstate, bismuth nitrate, citrate and nitric acid as the starting materials. The structure and morphology of as-synthesized Bi₂WO₆ samples were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM). Thermogravimetry and differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR) were applied to analyze the thermal behavior of the Bi₂WO₆ precursor. There are four stages were found in the TG-DTA curves of the Bi₂WO₆ precursor, and the Bi₂WO₆ started to be formed at 367 ℃ in the third stage. The pure bismuth tungsten oxide powders were prepared by calcination of the precursors at 400~700 ℃ for 5 h. The spherical particle size of Bi₂WO₆ powders does not change apparently with increasing temperature below 600 ℃. The grain grow up rapidly and orthogonal crystal system obtained when the temperature at above 700 ℃. The crystal grow process of Bi₂WO₆ undergoes a transition from a diffusion control mechanism to an interfacial reaction controlled mechanism as the temperature increasing. The morphology and size can be controlled by setting the calcination temperature and the soaking time.