In the design of actively controlled structures, the determination of the actuators and sensors location is a very important issue. In this way, the purpose of this paper is to propose a new approach to find the optimal location of piezoelectric actuators and sensors on beam structures. More precisely, first the optimization criteria are defined: it is proposed here to find the optimal actuators location by minimizing the mechanical energy integral of the system and the optimal sensors location by maximizing the energy of the state output. In the two cases, a sensitivity method applied to the discrete equations is used. Several results are presented. This methodology is used to find the optimal location of one actuator and one sensor on a cantilever beam, and on a three-beam structure. When there are different optimal locations, several performance measures are considered in order to keep one location.