The Nuclear Protein Fractionation Kit provides an optimized cell extraction buffer, protease inhibitor cocktail, and Phosphatase inhibitor for convenient extraction of nuclear proteins from mammalian tissues and suspension or adherent culture cells. The extracted nuclear proteins can be used for many downstream applications such as Western blotting, ELISA, 2D electrophoresis, IP, EMSA, Pull down, transcription regulation nuclear enzyme assays. The procedure is simple, no ultracentrifugation and toxic chemicals are involved. The kit is sufficient for 50X10^7 suspension or adherent culture cells or 50x200mg of mammalian tissue samples.