Titanium dioxide (TiO2) nanocrystals of different shape were successfully synthesized in a new microemulsion system through a solvothermal process. The TiO2 nanocrystals were prepared from the reaction of tetrabutyl titanate (TBT), H2O, and oleic acid (OA), which were used as solvent and surfactant at 300∘C and 240∘C in a stainless steel autoclave. The sphere, polygon, and rhombus-shaped nanocrystals have been prepared at 300∘C and the dot- and- rod shaped nanocrystals have been synthesized at 240∘C. The effect of the reaction time on the shape and size of TiO2 nanocrystals in this method was studied in the present paper. The size distribution of TiO2 nanocrystals prepared at 300∘C for different hours is also studied. In addition, an attempt to describe the mechanism of shape change of TiO2 nanocrystals was presented in this paper.