The present invention may provide a method of removing red blood cells and a centrifuge tube for blood collection, which method and centrifuge tube can, when cells contained in blood are observed after spreading the cells, improve detection accuracy of rare cells contained in the blood, hardly causing loss of the rare cells. The method of removing red blood cells may include the steps of: (A) fixing cells contained in a blood-derived sample and (B) subjecting the blood-derived sample obtained in the Step (A) to density gradient centrifugation to separate the sample into at least two layers, one of which contains a large amount of red blood cells and the other of which contains a large amount of cells other than red blood cells.
