Titanium dioxide nanoarchitectures with well-defined morphologies have been successfully synthesized by a hydrothermal process at temperature 180 °C for 4 h using titanium butoxide, oleic acid and hydrochloric acid as precursor materials. Different hierarchical morphologies such as cauliflower, 3D microsphere, densely-packed nanorod array, step edge faceted nanorod, branched structures of the rutile TiO₂ nanostructures could be easily controlled by varying the volume fraction of the added hydrochloric acid. The structural, photoluminescence and field emission properties of the as-prepared nanoarchitectures were investigated. Among the different morphologies, dense nanorod arrays and multilevel branched architectures showed good field emission properties. Morphology, surface-related defects and oxygen vacancies were found to be the major responsible factors for the observed variations of field emission properties. Compared to any previously reported TiO₂ based field emitter, lower turn-on field at 2.76 V μm⁻¹ and higher field-enhancement factors 7.44 × 10³ were observed for the hierarchically dense TiO₂ nanorods array. Therefore, these nanoarchitectures can be used in vacuum microelectronic applications.