Peroxynitrite,　which　is　cytotoxic,　can　modify　DNA　bases　and　make　DNA　single　strand　breaks.　In　this　paper,　the　reaction　of　DNA　and　peroxynitrite　was　studied　through　HPLC-ECD　and　agarose　electrophoresis.　The　results　showed　that　the　deoxyguanosine　modification　and　DNA　strand　breaks　upon　the　concentration　of　peroxynitrite.　Then　inhibitory　effects　of　some　crude　inhibitors,　such　as　quercetin,　flavone,　α-naphthoflavone,　caffeic　acid,　L-gluathione,　lipoic　acid　on　DNA　damages　was　investigated,　too.　The　results　indicated　the　inhibitory　effects　of　quercetin　and　caffeic　acid　were　more　effectively　than　that　of　flavone　and　α-naphylflavone;　and　the　DNA　damages　can　be　inhibited　by　the　compounds　containing　-　SH　group　(e.g.　L-glutathione,　lipoic　acid).