The main propulsion system may be the most complicated of the shipboard systems. Many factors such as fuel economy, weight, space, first cost, reliability, vibration and noise must be considered when selecting the prime mover of the main propulsion system for ships. An expert system is a computer program that represents and reasons with knowledge of some specialist subject with a view to solving problems or giving advice. Recently, it is being developed increasingly with wider applications in many industries. This paper describes development of knowledge-based system for main engine selection of ships using general purpose expert system development tool, Nexpert Object. Developed system is consist of ship performance estimation module such as resistance and propulsion, data base for main engine, knowledge base for main engine selection in Nexpert Object and graphic user interface.