A prototype knowledge-based system that assists plant site engineers in power maneuver planning for boiling water reactor (BWR) startup and load-following has been developed. In the conventional method, engineers formulate these plans based on their own expertise and on core simulation programs that require long running times. To more quickly provide a suitable plan, the new system makes an initial plan and modifies it based on both expertise stored in a knowledge base and simplified programs using a one-point BWR core model. The time required for this system is <30 min. The system was tested for 1100 -MW(electric) BWRs. The quality of the plans generated by the system is almost the same as that of plans directly generated by experts. The test results show that the system is useful in preparing a suitable plan efficiently and quickly.