The object of the invention is to provide an organic polymers-separation membrane filter capable of physically separating organic polymers based on their molecular stereostructure difference without giving rise to chemical changes in them and without selecting their chemical compositions. The organic polymers-separation membrane filter comprising an ultrafilter membrane is characterized in that a path taken by a nano permeation pore has a narrower path portion having a width narrower than that of the rest, wherein organic polymers capable of changing in their stereostructure are passed through the path while their width is transformed into a configuration along the narrower path portion, thereby separating the organic polymers. In the ultrafilter membrane, particulate materials are mutually coupled together in its thickness and planar directions. The particulate materials comprise a protein. The particulate materials comprise protein particles deposited onto a nanostrand such that they are mutually crosslinked and integrated together. The nano permeation pore includes a mark remaining where the nanostrand is removed. The invention also provides a method for separating organic polymers capable of changing in their stereostructure, using the organic polymers-separation membrane filter.
