In recent years, human embryonic stem cells have been established, and somatic stem cells derived from various adult organs have been identified and characterized to differentiate into various kinds of functional cells. There have been attempts to use functional cells induced from such stem cells for tissue regeneration and cell therapy. The method is expected to become an important treatment for intractable diseases in the near future. Since tissues and organs generally contain only a small quantity of somatic stem cells, and since it is necessary to separate functional cells generated from stem cells for use in therapy, an effective method for specific cell separation is crucial to the practical application of regenerative medicine. For the specific separation of cells, a fluorescence activated cell sorter using specific antibodies is a powerful tool, but the method is not suitable for large-scale processing and a special device is required. Although a magnetic cell separation system using immuno-magnetic fine particles is also commercially available, the system still needs special apparatus for large-scale processing. We developed a novel method for the separation of specific cells in an aqueous two-phase system using antibodies modified with a temperature-responsive polymer. The method enables the processing of a large quantity of cells without the requirement of a special device.