The study presents an inundation damage estimation method which quantifies the uncertainty in inundation damage statistical data for urban drainage management. The flood damage is usually estimated by multiplying inundated asset value by damage rate determined by the inundation depth. The dispersions of the asset values and the damage rates related to the uncertainty were expressed quantitatively using probability distributions for the actual flood damage data surveyed by the national government. Monte Carlo simulation was utilized to calculate the damage from the two parameters with probability distributions. Thus the simulations brought about the monetary flood damage not in deterministic but in probabilistic form.