The present invention relates to a method for in vitro expansion of mature erythroid cells. More specifically, the present invention relates to a method for obtaining concentrated erythrocytes by culturing erythroid cells at high density so as to allow the cells to physically and directly come in contact with each other. Particularly, the method of the present invention is very useful in that it is possible to obtain a large amount of clinically useful concentrated erythrocytes through a small container such as a test tube-sized bioreactor.