When the length of an annular liquid film in a circular pipe exceeds a critical length under zero gravity, the liquid film breaks into several lobes periodically, and plugs are formed. The behaviors of the interface deformation of the liquid films and plug formation under microgravity were investigated. using the drop-shafts of Hokkaido National Industrial Research Institute (HNIRI), Microgravity Laboratory of Japan (MGLAB) and Japan Microgravity Center (JAMIC). The glass pipes were installed horizontally and vertically. The experimental and numerical results of the average wavelength of the lobes spaced along the pipe were in good agreement with those of the linear stability analysis.