In situ X-ray diffraction patterns of the powder titania polymorphs are recorded in a temperature range from room temperature (RT) to 1200℃ in static air and vacuum. The results show that the temperature converting anatase into rutile is at 850℃ in static air and at 855℃ in vacuum. Lattice parameters for anatase (RT-850℃) and rutile (RT, 900-1200℃) in static air and those for anatase (27-850℃) and rutile (950-1200℃) in vacuum are refined. The variations of lattice parameters of anatase and rutile with temperature (℃) are therefore well described. Linear () and volume () thermal expansion coefficients of anatase (RT-850℃) and rutile (RT, 900-1200℃) are calculated. The change laws of and with temperature for anatase and rutile in static air and vacuum are summarized. At RT, the thermal expansion coefficients for anatase are a=4.5506310-6/℃, c=7.754310-6/℃, and =16.8583610-6/℃ in static air and a=4.6942910-6/℃, c=9.0285010-6/℃, and =18.6968810-6/℃ in vacuum while those for rutile are a=6.8124310-6/℃, c=8.7164410-6/℃, and =22.2217810-6/℃ in static air and a=6.0583410-6/℃, c=8.3928010-6/℃, and =20.5236210-6/℃ in vacuum, respectively.