Abstract: With the presence of time-delay and packet dropout effects in the network,the problem of robust fault detection for a class of nonlinear networked control systems is investigated.Based on a nonlinear networked control system model approximated by uncertain T-S fuzzy models,the robust fault detection observer is designed under network environment such that the residual signal is sensitive to the fault but robust to exogenous disturbance.Sufficient conditions for asymptotically stability of the observer-based estimation error system is established by constructing the Lyapunov-Krasovskii functional candidate and introducing an integral inequality.The robust fault detection problem is formulated as convex optimization problem subject to linear matrix inequalities.Simulation results show the effectiveness of the proposed method to handle robust fault detection problem for this kind of nonlinear networked control systems.