It is difficult to perform the subdivision design of tanker automatically because a lot of restrictions such as total tank capacity, segregated ballast tank capacity, limitation of each tank size, trim, strength etc. must be considered simultaneously. Human designer makes it in following way : (1) assume a temporary design, (2) evaluate it, (3) change it so as to satisfy restrictions and to come nearer to optimum, (4) repeat 2 and 3 until satisfactory design is obtained. In this approach, designer's know how of redesign is essential. Application of AI or knowledge engineering is very helpful to support stepwise and heuristic approach like this.In this paper, expert system prototype for subdivision design of tanker was built to see the effectiveness of AI in this field. The system was composed of three subsystem which are production system, frame system and user interface system. Production system controls the basic loop of evaluation and redesign. It handles human designer's know how of redesign as if-then rules. Each rule describes the know how of “If (condition of evaluation results), then (redesign procedure).” Design object model including design parameters, restriction conditions, optimization indeces and the relationships among them was represented as frame. Frame system handles it to support redesign powerfully with automatic recalculation of related parameters. User interface system was very important not only in using the completed system but also in if-then rule acquisition for system development. It was shown that the expert system could design the subdivision of conventional tankers from 100, 000 DWT to 240, 000 DWT automatically with satisfaction.