The effect of three levels of zirconia (ZrO2) additive on the anatase-rutile (A-->R) transition in a sol-gel-derived powder was investigated using differential thermal analysis and X-ray diffraction. The ZrO2 additive was found to retard the A-->R transition. The formation of a limited solid solution of ZrO2 in TiO2 (solubility less than Zr/Ti = 0.075) at relatively low temperature, which probably increases the strain energy of TiO2 particle, is responsible for the increased transition temperatures. The apparent activation energy of A-->R transition in the presence of ZrO2 additive (Zr/Ti = 0.05) was determined as 468 kJ/mol.