The finite width of the plateau in the Hall resistance is studied quantitatively. If we gave a filling factor V , the ratio of the plateau width L I B to the center of the plateau BH square is constant f o r all other filling factors V' i j u'=u+m with m any integer. The temperature dependence of the plateau, width is also studied. Theoretical results ase in goad agreement with the data obtained j r o m expe ram e nt .