A decision support system is introduced for the efficient operation of port container terminals. It consists of ship planning subsystem, yard planning subsystem, resource management subsystem, real-time control subsystem, and simulation subsystem. The system is intended to support the planning process of the planners and the operation process of the administrators in the container terminals. It is assumed that the transfer cranes and the yard tractor/trailers are used to handle containers in the marshaling yard. The system is explained in terms of the functions of each subsystem and the data flows among various subsystems.