A power generation control system includes a converter and a controller. The converter controls a generator of a Rankine cycle system, the Rankine cycle system including an expander, the generator, which is interconnected to the expander, a pump which feeds a working fluid, and an evaporator which evaporates a working fluid. The controller causes the converter to execute, in at least one of a startup operation and a shutdown operation of the Rankine cycle system, first control in at least one of a startup operation and a shutdown operation of the Rankine cycle system such that the expander is prevented from expanding a working fluid if the working fluid at an outlet of the evaporator contains a liquid component while the pump is operating.