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