An operation control system for a planing boat can include a mode selection module configured to allow a driver to select a driving mode of either one of a normal operation mode, in which the boat cruises at a speed in response to the displacement of an acceleration controller, and a speed-fixing mode, in which the boat cruises at a fixed speed at a level when a speed-fixing controller is operated. The system can also include a planing condition determination module configured to determine whether a hull is at the stage of planing, in which the mode selection module is configured to prohibit the driving mode from switching to the speed-fixing mode if the planing condition determination module determines that the hull is not at the stage of planning. The mode selection module can also be configured to permit the driving mode to switch to the speed-fixing mode if the planing condition determination module determines that the hull is at the stage of planing.