Discussing about frictional mechanism between two solids, it is very important to observe the contact states between the solids during friction. Concerning about friction of rubber, because rubber around contact surface should be deformed by friction, frictional force of rubber depends on not only area of contact but also deformation of rubber around contact surface. A lot of rubber products, for example tires, roller for paper handling and so on, are rubbed against rough surface, and usually they are opaque. Thus it is difficult to observe contact states during friction by visible ray. In this paper, we introduce studies on observation of contact states between rubber and mated surface using X-ray Imaging method. The frictional force shows a correlation with the contact area or the shear stress of the rubber. Consequently, it was summarized that the real time observation during friction using X-ray imaging is very effective to understand the mechanism of rubber friction.