Disclosed is a humidifier for fuel cell including a membrane housing including a first end, a second end positioned at an opposite side of the first end, and plural holes provided along the outer circumferential surface of the second end; hollow fiber membranes having both ends respectively potted into the first and second ends of the membrane housing, wherein the hollow fiber membranes are positioned inside the membrane housing; and a cap including an inlet for moisture-containing unreacted gas, wherein the cap is installed at the second end of the membrane housing, and an inner surface of the cap is provided with plural projections enabling the moisture-containing unreacted gas supplied through the inlet to be uniformly distributed to the plural holes.