A single-step sonochemical method to directly prepare rutile nanocrystal TiO2 has been developed. TiO2 nanaoparticles were synthesized by the hydrolysis of TiCl4 in the presence of water and ethanol under ultrasonic irradiationat 70 °C for 3 h. The crystalline forms and crystallite sizes of the produts were characterized by X-ray diffraction, transmission electron microscopy and thermogravimetry-differential thermal analysis. The TEM images showed the morphology of as-prapared TiO2 was pinnate in shape and the average sizes were ca. 4/12 nm (W/L). The columnar particles were linked together each other at the certain principle, forming the shape like dendrite crystal. The formation mechanism of the dendrite crystal nanocrystalline TiO2 was also discussed.