Abstract: The present invention aims to provide a porous separation membrane that does not suffer a significant decrease in the protein permeability even after long term use. The porous separation membrane has an asymmetric structure with a dense layer forming one surface layer and with a coarse layer forming the other surface layer, supports a biocompatible polymer, and meet the requirements (1) and (2) given below in surface analysis of a cross section containing the dense layer and the coarse layer performed by TOF-SIMS: (1) the minimum value of normalized intensity of the ion signal attributed to the biocompatible polymer in the coarse layer is 0.15 times or more of the maximum value, and (2) the normalized average intensity of the ion signal attributed to the biocompatible polymer in the dense layer is 2.0 times or more of the normalized average intensity of the ion signal attributed to carboxylic acid in the coarse layer.

Abstract: Disclosed is a porous hollow fiber membrane containing a polysulfone-based polymer as a main component, which has an asymmetric structure in which the inner surface side is dense and the outer surface side is coarse, wherein an average of a minor axis diameter of pores of an inner surface is 20 nm or more and 40 nm or less, an open porosity of the inner surface is 10% or more and 30% or less, and a polymer including a monocarboxylic acid vinyl ester unit is supported on at least one of the outer surface and the inner surface. The present invention provides a hollow fiber membrane which has excellent removing performance of substances to be separated such as viruses, and can be used as a separation membrane having high permeability even in a treatment under low pressure.