Uniform nanoparticles of rutile and anatase were prepared, respectively, by a new approach, a microemulsion-mediated method, in which the microemulsion medium was further treated by hydrothermal reaction. Herein, the combined procedure of microemulsion and hydrothermal synthesis to prepare nanoparticles is referred to as a microemulsion-mediated hydrothermal (MMH) method. This MMH method could lead to the formation of crystalline titania powders under much milder reaction conditions than the normally reported microemulsion-mediated methods, in which posttreatment of calcination was necessary. In this work, a kind of solution was formed by dissolving tetrabutyl titanate into hydrochloric acid or nitric acid, and the solution was dispersed in an organic phase for the preparation of the microemulsion medium. The aqueous cores of water/Triton X-100/hexanol/cyclohexane microemulsions were used as constrained microreactors for a controlled growth of titania particles under hydrothermal conditions. The product of hydrothermal synthesis was separated and dried for characterization. The phase components and the morphologies and grain sizes of products were determined by X-ray diffraction (XRD) and by transmission electron microscopy (TEM). The effects of changing the variables of the reaction conditions, such as the use of acid, the concentrations of acid, the reaction temperatures, and/or the reaction times on the phases and morphologies of the titania product are described.