In this paper, stochastic optimal controllers of networked control systems whose network-induced delay is longer than a sampling period are designed for the two cases of the system with either full state information or partial state information. The controllers are shown to render corresponding networked control systems exponentially mean square stable. The optimal estimator of the system state is presented when the system has partial state information and network-induced delay is longer than a sampling period. The separation theorem is proved to still hold in such networked control systems. (C) 2003 Elsevier Ltd. All rights reserved.