Abstract— This paper presents an application of deploying an adaptive state-space feedback controller for vibration suppression in a flexible cantilever beam system using single and multiple control actuators and deflection sensors optimized with an On-line Particle Swam Optimization (PSO). The PSO is adopted for the optimization problem because of its proved simplicity and performance in different linear and nonlinear applications. Neither expensive computations nor specialized methods are needed. The behavior of the complex nonlinear beam system makes it difficult to locate a global minimum. This nonlinear vibration problem is equivalently changed to the problem of function optimization, which is tackled by using PSO, where a population- based stochastic optimization technique inspired by the social behavior of bird flocking is used, The approach is validated using numerical simulations; and the results confirm the effectiveness of the PSO approach and its ability to highly improve the vibration cancellation performance of the flexible beam system.