A control system of an internal combustion engine includes a port injection valve and an electronic control unit. The electronic control unit is configured to: (i) obtain one of a start crank angle and an end crank angle, (ii) calculate the other of the start crank angle and the end crank angle, based on an equation for calculating a provisional injection amount of the case where the port injection valve provisionally injects the fuel with the one of the start crank angle and the end crank angle and a given crank angle range; (iii) convert a crank angle range from the start crank angle to the end crank angle, into a target energization period; and (iv) perform fuel injection by energizing the port injection valve for the target energization period.