Abstract: There is disclosed a novel porous hollow fiber membrane which is characterized by such a unique porous structure that the inner and outer membrane surfaces have an in-a-plane average pore diameter of 0.01 to 10 .mu.m and the porous membrane wall has an in-a-plane porosity of not less than 10% measured in every plane perpendicular to a radial direction of the annular cross-section of the hollow fiber membrane, wherein the in-a-plane porosity exhibits at least one minimum value between the inner and outer membrane surfaces. The present porous hollow fiber membrane has been found to be especially useful for the removal of a virus from an aqueous protein solution containing a virus. A virus can be effectively removed from an aqueous protein solution with not only an extremely high virus removal percentage but also an extremely high protein permeability, without causing the protein to be denatured.

Abstract: There is disclosed a novel porous hollow fiber membrane which is characterized by such a unique porous structure that the inner and outer membrane surfaces have an in-a-plane average pore diameter of 0.01 to 10 .mu.m and the porous membrane wall has an in-a-plane porosity of not less than 10% measured in every plane perpendicular to a radial direction of the annular cross-section of the hollow fiber membrane, wherein the in-a-plane porosity exhibits at least one minimum value between the inner and outer membrane surfaces. The present porous hollow fiber membrane has been found to be especially useful for the removal of a virus from an aqueous protein solution containing a virus. A virus can be effectively removed from an aqueous protein solution with not only an extremely high virus removal percentage but also an extremely high protein permeability, without causing the protein to be denatured.