As a kind of two-dimensional (2D) nanostructured materials, metal oxide nanosheets (MONS) are attractive and promising humidity sensing materials due to their considerable surface area, good charge carrier transportation, and designable surface functional groups properties. Nevertheless, the ultra-thin MONS modified with active functional groups for humidity sensing are still rare. As a proof of concept, the atomically thin TiO₂ nanosheets with high surface area and electron-donating amino groups are prepared by a structure-maintained post-ligand modification strategy. The fabricated TiO₂-based sensors demonstrate superior humidity sensing performance with high response, short response time, narrow hysteresis, and ultra-low theoretical limit of detection of about 15 ppm. Additionally, the possible mechanism is proposed from the AC complex impedance measurements and DC instantaneous reverse polarity experiments. This work provides a possible path for developing the high-performance 2D nanostructured metal oxides-based humidity materials through the surface chemical method.