Three types of tetraalkyl ammonium hydroxides (TANOHs)—namely, tetramethyl ammonium hydroxide (TMNOH), tetraethyl ammonium hydroxide (TENOH), and tetrabutyl ammonium hydroxide (TBNOH)—were used as peptizing agents for the hydrothermal synthesis of nanocrystalline TiO2 powders. X-ray diffractometry, Brunauer-Emmett-Teller surface-area analysis, differential thermal analysis-thermogravimetry, scanning electron microscopy, and transmission electron microscopy were used to characterize the powders. The results showed that the carbon-chain length of TANOHs had a great influence on the particle size, particle shape, and the phase transformation of the hydrothermally derived TiO2 particles. Anatase phase was obtained in all the samples, regardless of the peptizer used, and the particle size increased as the peptizer cation size decreased. In the presence of TMNOH, the particle shape changed from spherical at low concentration to rodlike with increasing TMNOH concentration, whereas a transition from a spherical morphology to an asterisk-like structure was observed in the TENOH peptized samples. However, spherical particles were formed in all the TBNOH peptized samples. The anatase-rutile transition occurred at a lower temperature for the TENOH-derived powders, relative to the other two peptizers.