Power oscillations increase the risk of instability and reduce power quality after a power system is subjected to a disturbance. Recently, the static series synchronous compensator (SSSC) has shown its ability to improve power oscillation damping (POD). Because of the nonlinear dynamics associated with the SSSC, and effective interactions among its variables, conventional linear control techniques result in poor control performance. In this paper, a novel input affine nonlinear and multivariable model for a transmission line installed with an SSSC is developed. Then, a nonlinear multi-input multi-output (MIMO) feedback linearized controller is proposed to improve POD. Simulation results verify the validity of the offered model, and show that the proposed nonlinear controller can successfully diminish power oscillations. In addition, superior output tracking performances are achieved