NFATc2, also known as NFAT1 or NFATp, is a member of NFAT (calcineurin-dependent nuclear factor of activated T cells) family of transcription factors. As one of major targets for immunosuppressive drugs, NFATc2 has been studied largely in the context of T cell activation and proliferation. Recent evidence suggested that it has a broader role in both immune and non-immune systems in regulating cell cycle progression. Using a monoclonal antibody developed specifically against phospho-serine 170 (p-Ser170) of NFATc2, we show here that this phosphorylation marks the M phase of cell cycle both during embryonic development and in cultured fibroblast and ES cells.