The nucleation and growth of vanadium oxide nanotubes (VOx-NT) have been followed by a combination of numerous ex situ techniques along the hydrothermal process. Intermediate solid phases extracted at different reaction times have been characterized by powder X-ray diffraction, scanning and transmission electron microscopy, electron spin resonance, and V-K edge X-ray absorption near-edge structure spectroscopy. The supernatant vanadate solutions extracted during the hydrothermal treatment have been studied by liquid 51V NMR and flame spectroscopy. For short durations of the hydrothermal synthesis, the initial V2O5-surfactant intercalate is progressively transformed into VOx-NT whose crystallization starts to be detected after a hydrothermal treatment of 24 h. Upon heating from 24 h to 7 days, VOx-NT are obtained in larger amount and with an improved crystallinity. The detection of soluble amines and cyclic metavanadate [V4O12]4- in the supernatant solution along the hydrothermal process suggests that VOx-NT result from a dissolution-precipitation mechanism. Metavanadate species [V4O12]4- could behave as molecular precursors in the polymerization reactions leading to VOx-NT.