A liquid fuel cell system is disclosed. The liquid fuel cell system includes a liquid fuel cell unit and a liquid fuel cartridge that can be connected to the liquid fuel cell unit. The liquid fuel cell unit and the liquid fuel cartridge each include a valve unit. The liquid fuel cartridge is connected to the liquid fuel cell unit so as to pour and supply liquid fuel that is a methanol solution from the liquid fuel cartridge to the liquid fuel cell unit. Using the supplied liquid fuel, the liquid fuel cell unit generates power to charge a battery. After the charging, both of the valve units are opened to return the liquid fuel remaining in the liquid fuel cell unit back to the liquid fuel cartridge, and thus, the liquid fuel cell unit is emptied.