The invention relates to a hollow fiber membrane module comprising polysulfone type selectively permeable hollow fiber membranes which contain a polysulfone-based resin and a hydrophilic polymer as main components, wherein (A) the content of the hydrophilic polymer in the uppermost layer of the inner surface of the hollow fiber membrane is at least 1.1 times larger than the content of the hydrophilic polymer in the proximate layer of the inner surface of the membrane, and (B) the content of the hydrophilic polymer in the uppermost layer of the outer surface of the hollow fiber membrane is at least 1.1 times larger than the content of the hydrophilic polymer in the uppermost layer of the inner surface of the membrane. The hollow fiber membrane module is exposed to a radioactive ray, on condition that the oxygen concentration of an ambient atmosphere around the hollow fiber membrane is from 0.001 to 0.1%, and that the moisture content of the hollow fiber membrane to the weight thereof is from 0.2 to 7 mass %.