Nanotubes are generally prepared from their constituent elements at high temperatures, and thus it is difficult to control their size, shape and electronic states. One useful approach for synthesizing well-defined nanostructures involves the use of building blocks such as metal ions and organic molecules. Here, we show the successful creation of an assembly of infinite square prism-shaped metal-organic nanotubes obtained from the simple polymerization of a square-shaped metal-organic frame. The constituent nanotube has a one-dimensional (1D) channel with a window size of 5.9 x 5.9 angstrom(2), and can adsorb water (H(2)O) and alcohol vapours, whereas N(2) and CO(2) do not adhere. It consists of four 1D covalent chains that constitute a unique electronic structure of 'charge-density wave (CDW) quartets' on crystallization. Moreover, exchanging structural components and guest molecules enables us to control its semiconductive bandgap. These findings demonstrate the possibility of bottom-up construction of new porous nanotubes, where their degrees of freedom in both pore space and framework can be used.