The safe disposal of high-level radioactive waste has become a prominent global concern, necessitating rigorous safety assessments for deep geological disposal facilities. In Korea, crystalline rock with low-permeability is considered as the host rock for radioactive waste disposal, and fluid flow and solute transport in a low-permeability rock formation predominantly occur through interconnected fracture network. To analyze and predict fluid flow and solute transport behavior within the fractures, a comprehensive understanding of solute mixing at fracture intersections is crucial. However, difficulty in direct observation of the mixing processes occurring within microscale fracture intersections has led only to analytical and numerical studies, which requires thorough experimental study based on direct observations and measurements for a fundamental understanding of the mixing processes in fracture intersections. In this study, elaborate experiments are being prepared and conducted to measure the complex flow velocity/structure and solute concentration at rough-walled fracture intersections, using a microscale visualization technique of micro Particle Image Velocimetry (micro-PIV) system. Most analytical and numerical studies have shown that at high Peclet number (Pe) > 1,000, streamlinerouting model plays a major role in redistributing solutes at the fracture intersection, at which the mixing ratio converges to zero. As opposed to the conventional mixing model, our experiments found the rebounding of the mixing ratio in the inertial flow regime, indicating an enhanced solute mixing at the intersection. Flow visualization has demonstrated that the inertial flow features, such as the development of large-scale eddies and the straightening of main streamlines, enhance the physical mixing of solutes at rough-walled fracture intersections. The findings provide insights into the influence of fracture geometry on flow dynamics and its significant impact on solute mixing at fracture intersections.