A new controller design problem of networked control systems with packet dropping is proposed. Depending on the place that the observer is put in the system,the network control systems with packet dropping are modeled as stochastic systems with the random variables satisfying the Bernoulli random binary distribution. The observer-based controller is designed to stabilize the networked system in the sense of mean square,and the prescribed H_∞disturbance attenuation level is achieved.The controller design problem is formulated as the feasibility of the convex optimization problem,which can be solved by a linear matrix inequality (LMI) approach. Numerical examples illustrate the effectiveness of the proposed methods. A new controller design problem of networked control systems with packet dropping is proposed. According to the place that the observer is put in the system, the network control systems with packet dropping are modeled as stochastic systems with the random variables satisfying the Bernoulli random binary distribution The observer-based controller is designed to stabilize the networked system in the sense of mean square, and the prescribed H_∞disturbance attenuation level is achieved. The controller design problem is formulated as the feasibility of the convex optimization problem, which can be solved by a linear matrix inequality (LMI) approach. Numerical examples illustrate the effectiveness of the proposed methods.