PURPOSE: To obtain a composite hollow fiber membrane having a thin membrane sepn. layer free of pinholes and gaps by applying a dilute soln. of a membrane forming material on a porous hollow fiber substrate, then partially drying the coating and further bringing the substrate into contact with a solidifying soln. to induce the removal of a solvent and solidification.

CONSTITUTION: The dilute soln. consisting of the membrane forming material, such as cellulose acetate or brominated polyphenylene oxide and a solvent for the material is applied on the surface of the porous hollow fiber substrate. Next, the solvent in the coating film is partly evaporated and partially dried in a gaseous atmosphere. Further, the coating film is brought into contact with the solidifying soln. to solidify the membrane forming material on the surface of the porous hollow fiber substrate described above and the solvent is dissolved into the bath. The thus resulted composite hollow fiber membrane has the uniform and thin membrane sepn. layer free of the gaps and pinholes. The adoption of the solvent and substrate which are heretofore unsable on account of the adverse influence at the time of dry removal of the solvent in the conventional method is made possible with this method.