The TiO2 nanoparticles with high photocatalytic activity were prepared by the surfactant-free microemulsion (SFME)-hydrothermal method at lower temperatures using oil-in-water SFME systems as templates. The phase diagram of the SFME ethyl acetate (EA)/propan-2-ol/water was determined by electrical conductivity and UV-visible spectroscopy. The synthesized TiO2 nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, and N-2 adsorption-desorption techniques. They were all assigned to the anatase phase and showed type IV adsorption-desorption isotherms with type H2 hysteresis loops. As the EA content (f(o)) of the SFME decreases, the Brunauer-Emmett-Teller (BET) specific surface area (S-BET) of the TiO2 nanoparticles increases. This results in an increase in the photocatalytic activity of the TiO2 nanoparticles. With an increase in temperature, the photocatalytic activity of the TiO2 nanoparticles increases significantly, whereas the SBET values decrease and the crystal size increases. Under the same conditions, the degradation rate of the TiO2 prepared at 190 degrees C reaches 97%, which is significantly higher than that of Degussa P-25 (66%). This may be due to the use of the SFME system to synthesize the TiO2 nanoparticles, which avoids the blocking effects of surfactant molecules on the active sites of the nanoparticles.