This paper develops a novel self-tuned fuzzy damping control scheme for an interline power flow controller (IPFC) to suppress the interarea mode of oscillations in a multimachine power system. The nonlinear adaptive damping controller is based on coordinated operation of two fuzzy inference systems. The first one produces the required q-axis voltage reference of the quasi multipulse series converter in response to generator angle oscillations, while the second one is used to tune the output of the first one online for further reducing the error signal using a given set of fuzzy rules. The simplex method is employed to search for optimal gains of the damping controller by minimizing the objective function in which speed deviations between generators are formulated. The feasibility of the proposed technique is validated using time-domain simulation cases in the PSCAD simulation program. It is also shown that the proposed damping scheme for IPFC works better than the static synchronous series compensator, which utilizes the same damping scheme in reducing the interarea mode of oscillations.