We report here a magnetically labeled feeder system for mouse embryonic stem/induced pluripotent stem (ES/iPS) cells. Magnetic attraction of feeder cells labeled with magnetite nanoparticles significantly increased ES/iPS colony-forming efficiency. Magnetic labeling of feeder cells also facilitated separation of ES/iPS cells from feeder cells. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.