A novel nanostructure of semiconductor quantum-well (QW) system is reported. The structure is a fine hollow tube with a micron-order diameter fabricated by rolling several tens of nanometers thick QW layer. For example, although the wall thickness is only 40 nm, the system retains the quantum properties of a QW, and the optical emission from the QW subbands can be clearly observed. In addition, even though the tube-wall thickness is much smaller than the light wavelength, high quality factor optical resonance based on a kind of the whispering gallery modes is observed, which will enable the system to be a new type of low-threshold semiconductor laser.