<p>The normal deformability of rock joints plays a crucial role on the mechanical behaviour of jointed rock masses, particularly in civil geo-mechanical applications such as rock slopes and underground structures. While much efforts have carried out to understand the mechanical behaviour of rock joints under shearing, estimation of the normal stiffness remains a debated topic for rock engineers. This study aims to investigate the impact of contact area on the normal stiffness of rock joints through an extensive set of experiments. Laboratory experiments were conducted on four natural joints with various roughness, replicated using three different types of rock-like materials. Normal deformability tests were performed on these joints, and contact area evolution was measured in these experiments. Results of the experiments show that the contact area is controlled by the applied normal stress, joint surface roughness and material type where the increase in surface roughness leads to an increase in contact area at a constant normal stress. The increase in joint surface roughness also results in a decrease in joint closure and enhanced normal stiffness due to increased interlocking. It was found that joints with higher joint wall strength exhibit greater normal stiffness at a constant stress ratio. A nonlinear correlation was found between the contact ratio and applied normal stress, joint wall strength and surface roughness. Results from this study clearly show that the contact area exerted the most significant influence on variations of joint normal deformability and enhances joint surface interactions and facilitating stress transmission under normal loading.</p>