The present invention provides a blood purifier which shows a decreased amount of hydrogen peroxide extracted from its selectively permeable separation membranes, and thus is highly reliable in its safety in use for hemecatharysis.The present invention relates to a blood purifier which comprises selectively permeable separation membranes as a main component and which is characterized in that the amount of hydrogen peroxide which is extracted from the selectively permeable separation membrane removed from the blood purifier after 3 months or longer has passed since the sterilization of the blood purifier by exposure to a radioactive ray and/or an electron ray is not larger than 10 ppm.
