The present invention relates to a fuel cell membrane humidifier having an improved coupling force between a potting portion and an inner case so that the coupling force can be maintained even when a fuel cell is repeatedly driven and stopped, the fuel cell membrane humidifier according to an embodiment of the present invention comprising: a humidification module for humidifying, with the moisture in exhaust gas discharged from a fuel cell stack, the air supplied from the outside; and caps respectively coupled to both ends of the humidification module. The humidification module comprises at least one cartridge including an inner case, a plurality of hollow-fiber membranes arranged in the inner case, the potting portion fixing the ends of the plurality of hollow-fiber membranes, and a laser bonding surface which is formed between the inner case and the potting portion through a laser bonding.