The inhibitory effect of phosphate on the crystal grain growth of nanosized titania during high temperature calcination was investigated. Nanosized titanium dioxide powders prepared by hydrolysis of titanium tetrachloride were soaked in phosphate solutions with different con-centrations. The obtained powders calcined at various temperatures were characterized by X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), and X-ray photoelectronic spectroscopy (XPS). The grain size of the samples without phosphate treatment in-creased quickly when calcined at high temperatures, while the grain size of the samples with phosphate modification increased slowly when calcined at the same temperature. This phenomenon implies that phosphate treatment plays an important role in inhibiting the crystal grain growth of titania. The possible mechanism of the inhibition effect of phosphate on titania is discussed.