Granulocyte removal method

The purpose of the present invention is to provide a simple, highly safe method with which it is possible to recover mononuclear cells stably and at high efficiency from body fluids including mononuclear cells such as bone marrow aspirate, peripheral blood, and cord blood and removing the granulocytes. The present invention provides a granulocyte removal method that feeds a body fluid at a linear velocity of less than 0.33 cm/min to a container housing cellulose acetate having a proportion of hydroxyl groups substituted by acetyl groups of 23-54% of the total hydroxyl groups so that the total surface area is 157-627 cm 2 .