PURPOSE: To obtain the title hollow fibers usable for blood dialysis, having a high water permeation rate, improved selective permeability, and uniform wall structure, by spinning a specific solution of a cellulose derivative under specific conditions.

CONSTITUTION: A cellulose derivative (C) is dissolved in a mixed solvent of 0.2W 20 wt.% of a nonsolvent for C and 99.8W80 wt.% of a nonvolatile organic solvent to give a solid content C of 20W35 wt.%. The resulting solution is spun through the sheath part of a sheath-core type spinneret at a temperature t expressed by the formula, and a liquid is fed from the core part to coagulate the solution. Thus, the following porous network structure is obtained: (1) The fiber wall thickness is 10W 70μ. (2) The pores contain no cavities having a diameter ≥0.5μ. (3) The average pore diameter is 10W500. (4) The swelling degree of the wall is ≥0.5.