The present invention relates to a fuel cell membrane humidifier, which improves binding force between a potting part and an inner case, and thus can maintain the binding force even if a fuel cell is repeatedly operated and stopped. A fuel cell membrane humidifier according to an embodiment of the present invention includes: a humidification module for humidifying air, supplied from the outside, with the moisture of exhaust gas discharged from a fuel cell stack; and caps, which are each coupled to the both ends of the humidification module. The humidification module includes at least one cartridge having: an inner case; a plurality of hollow fiber membranes placed inside the inner case; and a potting part which fixes the ends of the plurality of hollow fiber membranes, and which is filled in and coupled to the end part of the inner case.