Various long-period superstructures that appear in Al-rich TiAl are composed of three pairs of primitive cells, Ti2Al, Ti3Al, and Ti4Al, having periodic atomic arrangements in unique shapes of lean rhombi, fat rhombi, and squares, respectively, on the (002) Ti layers. These primitive cells can produce long-period superstructures such as Al 5Ti3, Al3Ti2, and h-Al 2Ti. The long-period superstructures play an important role in the operative deformation mode, configuration of dislocations, and related plastic deformation behavior in Al-rich TiAl, depending on the Al concentration. Fourfold ordinary dislocations, for example, often move as a group in the Al5Ti3 superstructure in the shapes of lean rhombi and squares embedded in the L10 matrix. In this study, the relationship between the periodic long-period superstructures and dislocation motion will be discussed from the viewpoint of anti-phase boundaries that form in each superstructure and their energies. The plastic deformation behavior in Al 5Ti3 and h-Al2Ti single-phase single crystals is also discussed.