The optimal tracking performance of single-input-single-output networked control systems over limited communication channels is proposed in this paper. The signal-to-noise ratio (SNR) constrained of communication channel is considered. The tracking performance is measured by the energy of the error variance response between the output of the plant and the reference signal. The optimal tracking performance is obtained by applying the H ₂ square error criterion and the spectral factorization technique. It is shown that the optimal tracking performance is constrained by the non-minimum phase zeros, the unstable poles of a given plant, the power spectral density of a given reference signal, and the SNR of a communication channel. The results obtained in this work explicitly show how the optimal tracking performance is limited by the communication parameters (SNR in this paper). Finally, computer simulations are performed to verify the analytical results.