A method of enriching side population (SP) cells existing in tissues at a low-density in a simple manner with a high purity is disclosed. The method of enriching SP cells according to the present invention comprises culturing cells containing SP cell traction separated from a mesenchymal layer ON a porous substrate having penetrating pores large enough to allow cells pass through the cells and recovering cells remaining ON the porous substrate after the culture. SP cells may be enriched to a still higher density by carrying out the method of enriching SP cells of the present invention in combination with other enriching method and as the method of the present invention does not cause any biological alterations in cells.
