In this study, optimal performance of the multi-input multi-output networked control systems (NCSs) is analysed. The systems are with a time-delay and channel noise constraints in the forward network channel, and encoding-decoding and quantisation constraints, and packet dropouts in the feedback network channel. By using the Youla parameterisation of a two-degree-of-freedom controller, a new and explicit expression of the optimal performance is derived. The optimal performance is obtained using the method of H 2 norm technique. The results show that the positions and directions of the non-minimum phase zeros and unstable poles of a given plant are related to the optimal tracking error. On the other hand, the optimal tracking error is dependent on channel noise, quantisation noise, encoding-decoding, time-delay, packet dropout probability and other correction factors. Finally, simulation results demonstrate the effectiveness of the proposed control scheme.