This paper employs the Particle Swarm Optimization (PSO) method to solve the problem of the optimal design of cascade stilling basins. PSO is a relatively recent heuristic search method whose mechanism is inspired by the swarming or collaborative behavior of biological populations. The objective of this research is to minimize the total construction cost of cascade stilling basins, which is a function of height of the falls and length of stilling basins, while ful_lling the hydraulic and topographical criteria. To illustrate the application of PSO, a benchmark design is taken from the work of Vittal and Porey [1] on a cascade stilling basin for the Tehri Dam, India