An engine control system, for controlling an engine of a jet-propulsion boat, includes a cavitation-control-mode determination unit, which starts a cavitation-control mode when an engine speed not faster than 3200 rpm is maintained for a predetermined time period. During a normal sailing operation, ignition timing is set by a first ignition-timing setting unit. Upon detection of a cavitation-control-mode by the cavitation-control-mode determination unit, an engine speed is raised up to a speed not slower than 3200 rpm, which makes an ignition-timing switching unit to select a second ignition-timing setting unit. The second ignition-timing setting unit retards the ignition timing for the normal sailing operation when the engine speed becomes 6500 rpm or faster. In addition to retardation of the ignition timing, a boost pressure control command upper-limit value is switched to a value at a startup operation, which is less than a value at the normal sailing operation.