Abstract: An object of the present invention is to provide a separation membrane for blood treatment excellent in blood compatibility and reduced in elution of nitric acid ion from an inner surface even if radiation sterilization is applied in a dry state and to provide a blood treatment device having the membrane incorporated therein. The present invention provides a separation membrane for blood treatment containing at least a polysulfone resin and polyvinylpyrrolidone, wherein a proportion of intermediate water present in water in a functional separation surface of the separation membrane is 40% or more at the time when the content of water reaches a saturation point by impregnating a dry-state separation membrane with water, a water content of the separation membrane is 10% or less, and the separation membrane is subjected to radiation sterilization.