A leukocyte-removing filter, characterized in that it comprises a filter material having a vertical permeation coefficient (kx) of 0.5×10−12 to 2.0×10−12 m2 and a ratio (ky/kx) of a horizontal permeation coefficient (ky) to kx of 0.5 to 1.5 and a method for removing leukocytes using said filter. The above leukocyte-removing filter has a higher leukocyte-removing performance per unit volume and also does not bring clogging nor increase of pressure drop.
