Nanocrystalline TiO2 particles were prepared by hydrothermally treating three different titanium alkoxide species, which were derived from (i) the hydrolysis of Ti(OPr)(4) and Ti(OBu)(4) (PT and BT, respectively) in the presence of HNO3, tetraethylammonium hydroxide (TENOH), or NH3. H2O; (ii) water-washed precipitates; or (iii) sols that were obtained from the precipitates by peptizing with HNO3 or TENOH, X-ray diffractometry, Brunauer-Emmitt-Teller (BET) surface area analysis, differential thermal analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy were used to characterize the powders. The results showed that peptization of the precipitate favored formation of the rutile phase and highly crystalline anatase under hydrothermal treatment. Particles of 100% rutile phase with high specific surface areas were obtained at a relatively low temperatures: room temperature, for HNO3-peptized ([H+]/[Ti] = 4) PT sample (BET surface area of 96 m(2)/g); 200 degrees C, for the HNO3-peptized ([H+]/[Ti] = 1) PT sample (BET surface area of 49 m(2)/g); and 240 degrees C for the HNO3-peptized ([H+]/[Ti] = 1) BT sample (BET surface area of 42 m2/g). Particles that contained highly crystalline anatase, together with a small portion of rutile, were formed in both TENOH-peptized samples. However, rutile was difficult to form, both in the water-washed precipitates and in the species that was hydrolyzed in the presence of HNO3, TENOH, and NH3. H2O. The peptization effect of the H+ ion mainly lies in the breakage of oxolation by attacking the electrophilic O atoms among Ti atoms, thus creating conditions for the formation of rutile or anatase nuclei, after structural rearrangement.