In this study, the problem of simultaneous and coordinated tuning method for thyristor-controlled series capacitor (TCSC) power oscillation damping controllers and conventional power system stabilizer (PSS) controllers in multi-machine power systems is considered. For a multi-machine power system, the tuning of the PSS and TCSC controllers is generally formulated as an objective function with constraints consisting of the damping ratio and damping factor. Using the linearized system model and the parameter-constrained nonlinear optimization algorithm, interactions among TCSC controller and PSS controllers are minimized. It is done by simultaneously optimizing, the parameters of the damping controllers using sequential quadratic programming technique. Simulation results of a two area multi-machine power system validate the effectiveness of the approach and its capacity in tuning multiple controllers in power systems simultaneously.