To provide a separation membrane for a plasma component which is excellent in fractional characteristic from an initial period when the flow of the plasma is begun in blood treatment by the separation membrane for the plasma component and maintains the performance for a long period of time.

This separation member is specified to 80% in the holding rate of the permeation coefficients of albumin (ALB), globulin (IgG) and total cholesterol (TC) after 120 minutes with respect to the permeation coefficients of the albumin (ALB), globulin (IgG) and total cholesterol (TC) after 15 minutes after the flow of the plasma to a hollow fiber membrane of 50 to 150 μm in the bore of the membrane is begun.