Titania (TiO2) is an important electronic ceramic material for use in diverse applications such as gas sensors, catalysts, dielectrics, and ceramic membranes. TiO2 exists as several polymorphic phases, most commonly as rutile or anatase, This paper investigates the microstructural evolution of anatase-based commercial TiO2 powders, with an average size of 100 nm, at high temperatures. These powders transform to the rutile structure at 1000 degreesC. The characteristics of the anatase-to-rutile transformation have been studied using transmission electron microscopy analysis, and new information regarding the nature and mechanisms of this polymorphic reaction has been revealed.