This paper introduces flexibility of SCOPE (System Configuration Of PowEr control system) which is a new architecture to realize flexible and reliable supervisory control for power systems. Energy Management Systems/Supervisory Control and Data Acquisition (EMS/SCADA) systems are usually geographically distributed and have hierarchical operational organizations. They are continuously changing in accordance with various requirements and varying environments. Therefore, they should be flexible enough to adapt to those changes quickly SCOPE classifies programs in conventional electric power systems into three hierarchical layers, i.e Application dependent part, Power system dependent part and Computer system dependent part. The power system dependent part realizes flexibility for changing of power system equipment and operational organization; by introducing an enhanced abstract function of object oriented technology. Therefore, SCOPE architecture enables EMS/SCADA systems to be flexible, and also enables to develop efficiently and economically. Through developing and evaluating a SCOPE prototype system, it has been confirmed that the flexibility of EMS/SCADA systems had been improved.