The segregation phenomena of binary granular mixtures in a horizontal rotating cylinder are investigated. For the sake of simplicity, the glass cylinder which is a half‐filled with binary mixture of glass particles is adopted. The mixture consists of the same volumes of small size (diameter:0.2mm) and large size (diameter:0.6mm) glass particles. The rotation speed dependence of the long time scale segregation phenomena is studied. In a low rotation speed region, the initial narrow bands, which consist of small particles, gradually combined with each other and finally form one large band. On the other hand, in a high rotation speed region the initial narrow bands never combine with each other. The segregation phenomena in our case is thought to be caused by the drift motion of small particles along a inner axial core.We propose a new type model for numerical simulation which is able to take account of both effects of surface flow and inner drift of small particles. This model can reproduce the consecutive segregation phenomena obatained in our experiments. © 2004 American Institute of Physics