Abstract: To investigate the scale effects of contact characteristics in rock joints, a series of numerical models for joint sets with different sizes are generated using the self-affine fractal enlargement method. Subsequently, the normal contact problems are solved using a discrete elastic-plastic normal closure model. The contact characteristics in rock joints are analyzed quantitatively, and the effects of lithology and roughness of rock joints are also investigated. The roughness of the self-affine enlarged rock joints decreases with size. Moreover, there is a close correlation between the contact area ratio and the asperity parameters of the composite topography. The scale effects of the contact area ratio can be attributed to the variation of the combined asperity parameters of the composite topography \eta R with size. Additionally, the plastic components of normal closures increase with the joint size. The plastic deformation has weakening effects on the size effects of the contact area ratio, but strengthening effects on the size effects of closure deformation. The hard rock joints have a stronger scale effect of contact characteristics than the soft rock joints, and the representative lengths are also longer. The roughness of the rock joints has a contrary effect on the scale effects of the normal closure deformation and contact area ratio.