There is disclosed a leukocyte removal filter material comprising a nonwoven fabric having polybutylene terephthalate fiber. The average fiber diameter of the nonwoven fabric is 0.9 to 1.5 μm, the formation index corresponding to a thickness of 0.3 mm of the nonwoven fabric is 15 to 70, and when the average fiber diameter of the nonwoven fabric is X and the specific surface area of the nonwoven fabric is Y, X and Y satisfy the following relational expression (1):Y≧−0.65×X+1.75 (1).
