We propose the principles and methodologies for developing an online and real-time simulation system for controlling and monitoring an intelligent manufacturing system. An online and real-time system is a system that always been dynamically connected to another system so if there is a changing in state within one system, the other system will be affected directly. The research focuses on the application of these principles and methodologies into a manufacturing system model that is developed. The combination of the two features (online and real time) and the possibility to add an intelligent feature (by using knowledge-based approach) into the online and real time system will lead to an improvement of manufacturing system performance, which will be more reactive, responsive, flexible and also saving time for making decisions if there are any changing or disturbances in the manufacturing system. In short this paper is mainly concerned with controlling and monitoring disturbance that is caused by deterioration in state, for example machine/resource breakdown. We aim at addressing two fundamental issues. The first issue is related to the existence of a gap between shop floor level systems in the form of programmable logic controllers (PLCs) and sensor at one level and scheduling databases such as material requisition planning (MRPII), enterprise resource planning (ERP) and simulation at the supervisory/managerial level. The second issue is related to the parallel interface of maintenance data collection and decision support with the production system. The development of hardware and software is presented to address the two issues. The hardware is a miniaturised/model of a manufacturing system that is controlled by a PLC, a supervisory control and data acquisition (SCADA) systems and a PC in real-time manner. The software is developed and used to monitor and control the miniaturised system in online and real-time condition.