The anatase‐rutile phase transformation in Ar–Cl2atmosphere has been investigated by X‐ray powder diffraction, thermogravimetry, and scanning electron microscopy. At 950°C the phase transformation in Ar–Cl2atmosphere is about 300 times faster than in air. The growth of crystals of rutile from the vapor phase has been observed. We also determined that anatase powders with adsorbed chlorine rapidly rapidly transformed to rutile and underwent a color change from white to gray when they were heated in Ar at