We have successfully prepared nanoribbons of blue potassium molybdenum bronze (K0.3MoO3) from hydrogen molybdenum bronze (H0.3MoO3) by using crystallite splitting induced by solid-phase transformation and subsequent selective growth under hydrothermal conditions. The obtained nanoribbons were single crystals with a size of ca. 100 mu m x 100 nm x 10 nm, well-elongated to the crystal b axis that corresponds to the conduction direction as a quasi-one-dimensional metal. A simple. deaeration procedure necessary for preparing a single phase of blue potassium bronze is also given.