In fractured rocks of low/negligible matrix permeability, fluid flow and mass transport dominantly occur within the connected fractures (Boutt et al. 2006). An accurate understanding of fluid flow and solute migration through fracture networks in rocks is a critical issue in many applications, such as underground nuclear waste repositories, CO2 sequestration, and enhanced geothermal systems. Rock fractures are typically rough-walled, and surface roughness determines the location and distribution of contacting asperities, causes fluid flow in tortuous paths, and reduces the overall fracture conductance (Boutt et al. 2006). It has been demonstrated that fracture surface roughness has a significant impact on fluid flow and transport processes in single fractures, and that the mechanical aperture of a rock fracture is usually larger than its hydraulic aperture (Tsang and Witherspoon 1983; Zimmerman and Bodvarsson 1996; Boutt et al. 2006; Li et al. 2008). However, the effects of this reduced hydraulic aperture (due to roughness) in local fractures on macroscopic fluid flow and solute transport in complex fracture systems are still not clear, and most previous studies assumed identical hydraulic and mechanical apertures in discrete fracture network models for simplicity (Min et al. 2004a; Baghbanan and Jing 2008; Zhao et al. 2011). Therefore, in this study, we simulated flow and transport processes in two different fracture networks, aiming to investigate the influences of local surface roughness of fractures on fluid flow and solute transport processes at the macroscopic scales of fracture networks.