Potassium titanate (KT) nanowires were synthesized by a one-step hydrothermal reaction between TiO2 and aqueous KOH solution. The effects of KOH concentration and reaction time on hydrothermal formation and KT nanowire growth were investigated. The nanowire growth mechanism was elucidated using a combined study of powder X-ray diffraction, and scanning and transmission electron microscopy. The results revealed that hydrothermal growth was initiated by the formation of amorphous-like Ti-O-K sheets in anatase. Increasing hydrothermal reaction time caused the transformation of anatase to Ti-O-K sheets, from which potassium hexa-titanate (K2Ti6O13) nuclei formed and grew to establish one-dimensional morphology through preferential growth along the b-axis. It was revealed that the hydrothermal reactions followed a quite different mechanism than the well-known calcination route. Potassium tetra-titanate (K2Ti4O9) crystals formed in the amorphous region using the hexa-titanate phase as a nucleation site for heterogeneous crystallization. Increasing the KOH concentration in the solution accelerated the hydrothermal reaction rate.