PURPOSE: Specific thin-film hollow fibers of regenerated cellulose are impregnated with a specific amount of a plasticizer and dried to produce the titled hollow fibers that is suitable for use in artificial dialysis membranes, because of their high permeation selectivity, improved permeability and out of roundness.

CONSTITUTION: A cellulose ester is extruded into hollow fibers and the hollow fibers are hydrolyzed with an alkali to give hollow fibers of regenerated cellulose with a ratio of an inner diameter to membrane thickness of less than 1/0.2 in a wet state. Then, the resultant fibers are impregnated with 50W150wt% of a water-soluble plasticizer such as polyethylene glycol of average molecular weight of 200W1,000 on the basis of the weight of the hollow fibers and dried so that the dimension in the fiber axis direction is kept at more than 95% and more than 90% in the fiber diameter direction in its wet state.