A blood treatment filter which includes a housing including an inlet and an outlet, and a filter unit for filtering blood containing erythrocytes, platelets and leukocytes as blood cell components is provided. The filter unit includes a main filter unit which substantially removes predetermined cell components from blood and passes the remaining blood cell components, and a pre-filter unit which is arranged at the up-stream side of the main filter and substantially does not remove blood cell components. The pre-filter unit has a permeability rate of 70 to 90% for micro particles having an average particle size of 6 µm which are contained in a suspension and passed by gravity.
