We report a process directly transforming 2D nanosheets into 1D nanotubes. Using unilamellar nanosheets as starting materials, we succeeded in obtaining titanium oxide, manganese oxide, and niobate nanotubes (1560 nm in diameter). The transformation was achieved in a simple procedure of an ion intercalation/ deintercalation procedure at ambient temperature. The intercalation of Na ions leads to stacking up of the colloidal nanosheets. The gradual deintercalation/extraction of Na ions in water changes the inter-sheet bonding character. The peeled off nanosheets naturally roll up into nanotubes. It is most likely to be a universal process and has outstanding potential in customized syntheses of nanotubes from a wide range of lamellar solids.