The rapid expansion of renewable energy (RE) generation is leading to severe problems related to the reliability of network operation. Power system security is threatened by increased uncertainties of RE outputs and reduced controllable resources. Therefore, it is important to evaluate the robustness of the system controllability in order to preserve system security against uncertainties of RE outputs. We refer to the robustness of the system in this context as ‘robust power system security’. This paper proposes a new formulation for evaluating the robust security region in controllable parameter space where the conventional N-1 security criterion suffices in the presence of uncertainties. We specify the confidence interval (CI) of uncertain parameters and obtain the worst case feasible region defined by a set of security constraints, which is a very new approach in the treatment of uncertainties. We use the minimum set of static constraints in the load dispatching problem with CI of RE prediction to evaluate the security region, which is referred to as the robust static security region (RSS) in this paper. The proposed method is useful to assess the degree of difficulty of system planning and operation from the viewpoint of the balance between controllable generator capacity and RE uncertainties. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.