With unique characteristics in band position and surface structure, TiO2 provides a variety of potential applications. It has typical applications as a photocatalyst decomposing organic pollutants and/or producing hydrogen by watersplitting, and as a smart material with self-cleaning and/or super-hydrophilic properties. It also draws great attention as an electrode material for light-sensitizers or electrochromophores, consisting of dye-sensitized solar cells or electrochromic devices, respectively. Recently, the reverse micelle process has widely been applied to the syntheses of size-controlled nanoparticles for various metals and semiconductors. The carboxylic acids or amines with long hydrocarbon chains form a stable reverse micelle array in nonpolar ethers, and the cavities inside these arrays possibly be used as nanoreactors for the synthesis of nanoparticles. Moreover, it has been wellknown that the carboxylic acids have strong binding affinity toward TiO2. 4,5 Thus, the carboxylic acids with long hydrocarbon chain would be an appropriate surfactant for the synthesis of titania nanoparticles. Nonetheless, the synthesis of TiO2 nanoparticle is still very complicated, and only a limited success has been achieved so far in controlling its shape and size. Under a typical synthetic condition, such as reflux of reactants in flask, the obtained titania nanoparticles are heavily aggregated and their crystallinities are not so high in most case. So far, the hydrothermal or solvothermal reaction has usually been applied for the syntheses of various metal oxides at relatively low temperatures. Since the reaction is performed at an elevated pressure, more crystallized and denser structures have been obtained at a given temperature. Thus, in this work, we combined the solvothermal technique and reverse micelle method to obtain more crystallized and monodispersed titania nanoparticles without aggregation. A 0.45 g of titanium isopropoxide (Ti(OPri)4) was added to a solution containing 0.50 ml of oleic acid and 10 mL of octyl ether (molar ratio of Ti(OPri)4 to oleic acid = 1 : 1). All the chemicals were purchased from Aldrich Chemical Co. The mixture was stirred a few hours, and the clear solution was transferred to a glass-lined autoclave. The temperature of autoclave was raised to 240-300 C with a rate of 5 C/ min, and held for 6 hr. During this anhydrous solvothermal reaction the Ti(OPri)4 was thermally decomposed to form TiO2, and the TiO2 nanoparticles were finally obtained as a form of colloidal suspension. The optimum reaction temperature for the formation of anatase TiO2 nanoparticle has been determined to 260 C, which is relatively high compared with that from other synthetic methods. Here, we believe that the absence of water during the solvothermal reaction retards the crystallization and grain growth of titania nanoparticle. The crystallite size of TiO2 nanoparticle, calculated from the XRD peak of anatase (101) by applying the Scherrer equation, was 4.4 nm. TEM image in Figure 1a shows that the prepared TiO2 nanoparticles are monodispersed primary particles basically free from mutual aggregation, and they are mainly spherical shape with a diameter of 4.5 ± 0.5 nm, which corresponds to the crystallite size calculated from XRD patterns. Figure 1b shows the high resolution TEM image for an individual titania nanoparticle. The uniform fringes with an interval of 0.35 nm, corresponding to (101) lattice spacing of anatase phase, were observed over the entire particle. This indicates the synthesized each nanoparticle consists of single anatase grain. To control the hydrolysis of Ti(OPri)4, two equivalents of water relative to Ti(OPri)4 were added to the precursor solution before the solvothermal reaction. Then, it was