Nucleases play a direct and important role in DNA fragmentation which is a hallmark of apoptosis. The nucleases involved in apoptosis are divided into two types:divalent cations dependent nucleases and divalent cations independent nucleases.The divalent cations dependent nucleases mainly include nuc18,DNaseⅠ,Ca^2＋/Mg^2＋ nuclease,Ca^2＋/Mn^2＋ nuclease, DNaseγ, nuc58 and nuc40;The divalent cations independent nucleases mainly include DNaseⅡ and DNaseⅡ like nucleases.Moreover,the effect of nucleases on chromatin DNA degradation and the mechanism of this process were discussed.