Recently, property damages and loss of life caused by natural disasters are increasing in urban area because of local torrential rainfall, which is mostly originated from recent global climate change. Acceleration of population concentration and increase of impervious area from urbanization worsen the situation. Therefore, it is highly important to consider system resilience which is the system’s ability to prepare, react, and recover from a failure (e.g., flooding). This study proposes a resilience-constrained optimal design model of urban drainage network, which minimizes total system cost while satisfying predefined failure depth and duration (i.e., resilience measures). Optimal layout and pipe sizes are identified by the proposed model comprised of Harmony Search Algorithm (HSA) for optimization and Storm Water Management Model (SWMM) for dynamic hydrology-hydraulic simulation. The proposed model is applied to the design of Gasan urban drainage system in Seoul, Korea, and the resilience-based design obtained is compared to the least-cost design obtained with no constraint on the resilience measures.