Abstract: The H_∞ guaranteed cost control problem of the networked control system with a proportional-integral(PI) controller is studied.For the quadratic cost function and the networked control system with networks existing both between the sensor and the controller and between the controller and the actuator,the conditions for the existence of the H_∞ guaranteed cost control can be obtained with Lyapunov theory and Linear Matrix Inequality(LMI),which can not only enable the closed-loop system to be stable,but also guarantee that its cost does not exceed a certain determinable upper bound.Furthermore,the design method of the H_∞ guaranteed cost controller is also presented.Finally,an example is given to illustrate the feasibility of the proposed method.