Abstract: The paper demonstrated the possibility to enhance the damping of inter-area oscillations using wide area measurement system （WAMS） based on a wide area adaptive supervisory controller （WAASC） which considers the wide-area signal transmission delays. Pade approximation approach was used to model the signal transmission delays. The delays were regarded as a parameter uncertainty with linear fractional transformation （LFT） approach. A wide area centralized damping controller based on the mixed-sensitivity linear matrix inequality （LMI） approach with pole-placement restriction was designed. The WAASC used the input information from phase measurement units （PMUs） in power systems and dispatched supplementary control signals to the local controllers. Balanced truncation method was used to reduce the orders of the plant and the controller. The performance of the WAASC was validated by frequency and time domain simulations on an IEEE 4-machine 2-area system. Simulation results prove that the system oscillations with the WAASC in place are always much better damped than without it if the time delays are below 1.0 s. Additionally, the WAASC ensures system stability even in case of cascading faults.