Provided are air humidification device and method for a fuel cell. The air humidification device and method for the fuel cell may cool an air compressor and air compressed by the air compressor and easily humidify air supplied to the fuel cell by mixing water with air and injecting the mixture into an inlet of the air compressor. In particular, the air humidification device and method may easily humidify air supplied to a cathode of the fuel cell by bypassing a portion of the compressed air from an outlet of an air compressor supplying air to the cathode of the fuel cell and simultaneously by injecting condensed water discharged from a fuel cell system into an inlet of the air compressor using the bypassed compressed air.