This paper presents a design method of time-delayed control systems. Because of the tremendous spread of computer networks, control strategies for time-delayed control systems are needed for network-based control systems (NBCSs) and other network applications. Although model-based or predictive control methods (like a Smith predictor) are often used for time-delay compensation, the performance often deteriorates when the value of time delay is uncertain. In these circumstances, a novel time-delay-compensation method based on the concept of network disturbance (ND) and communication disturbance observer (CDOB) has been proposed. The method has the same effectiveness for time-delay compensation as that of the Smith predictor. Furthermore, because the method works without delay-time model, it can be flexibly applied to many kinds of time-delayed control systems. In this paper, a design method of CDOB, considering the dynamic property of ND, is proposed in the situation of constant time delay. The dynamic property of ND leads to two design conditions of CDOB. Those design conditions are derived considering relationships between poles of CDOB and ND dynamics. Then, the actual design procedure of CDOB based on derived design conditions is presented in two different delay cases. The stability of the designed control systems is clarified by stability analysis. The validity of the proposed design method is verified by experimental results. Finally, we present experimental results in the case of random delay as an example of practical application of the time-delay compensation method to actual NBCSs.