This paper presents a power system stabilizer (PSS) for improving the performance of a multimachine system when the system is subjected to different types of disturbances. An adaptive proportional-plus-derivative-plus-integral (PID) PSS is proposed in this paper. In this technique, the controller parameters (proportional, integral, and derivative gains) are not fixed but they are varying according to the system operating conditions. The derivative of power angle, error in output power, terminal voltage, and error in power angle are selected to be the input signals to the proposed stabilizer. A weighting factors are assigned to these signals to obtain the best performance characteristics of each machine. The obtained computer results from simulation study are compared with those of a conventional lead-lag stabilizer.