A membrane humidifier is disclosed. The membrane humidifier may include: a housing in which a hollow fiber membrane bundle is mounted, the hollow fiber membrane bundle being formed by integrating a plurality of hollow fiber membranes; a potting portion fixing an end portion of the hollow fiber membrane bundle to the housing and coupled to an end portion of the housing so as to hermetically seal the housing; and a sealing member disposed between the housing and the potting portion and hermetically sealing the housing.