This study proposes a reliability-based approach for the design of rockfall protection fences. From rockfall simulations using the code Rockyfor3D is deduced the probabilistic modelling of the impact angle and impact velocity of rocks. A discrete element model represents a low energy fence (software Yade-dem). The probability for the failure of the fence is evaluated, on a real study case, using a collocation method, based on a limited number of impact simulations.