The present invention relates to a cartridge for a fuel cell humidifier, and a fuel cell humidifier, the cartridge comprising: an inner case having both ends opened; a hollow fiber membrane bundle received in the inner case; an inner inlet and an inner outlet formed on the inner case so as to be spaced along a first axial direction; a first potting layer for fixing one end of the hollow fiber membrane bundle at one end of the inner case; and a second potting layer for fixing the other end of the hollow fiber membrane bundle at the other end of the inner case, wherein the packing density is 0.405 to 0.625 inclusive, the packing density being based on, with respect to a second axial direction perpendicular to the first axial direction, the potting cross-section of the inside of the one end of the inner case where the first potting layer is potted, and the membrane cross-section of the hollow fiber membrane bundle.