A plasma purification membrane and a plasma purification system for
treating diseases. The above plasma purification membrane is a hollow
fiber plasma purification membrane being made of a hydrophobic polymer
and a hydrophilic polymer and having a sponge-like structure wherein the
pore size is continuously decreased from the outer surface of the
membrane toward the inner surface thereof, characterized in that the
break strength of the membrane is 50 kgf/cm.sup.2 or more and, in the
case of the inner pressure filtration of bovine plasma, the total protein
permeability is 50% or more while the immunoglobulin (IgM) permeability
is 90% or less.