A　solid-state　[Ru(bpy)(2)(dppz)](2+)　(bpy=2,2-bipyridine,　dppz=dipyrido[3,2-a:　2,3-c]phenazine)　electrochemiluminescence　(ECL)　biosensor　for　studying　the　binding　interactions　between　pesticides　of　heterocyclic　polycyclic　aromatic　hydrocarbon　(heteroPAH)　and　natural　double-stranded　DNA　(ds-DNA)　was　constructed.　Layer-by-layer　films　of　negatively　charged　natural　ds-DNA　and　polycationic　poly　(diallyldimethylammonium　chloride)　(PDDA)　were　assembled　on　the　surface　of　a　glassy　carbon　electrode　(GCE).　The　complex　of　[Ru(bpy)(2)(dppz)](2+)　was　used　as　a　probe.　Tripropylamine　(TPA)　was　used　as　an　electron　donor　to　chemically　amplify　the　ECL　intensity　of　the　probe.　If　the　xenobiotic　molecules　compete　with　the　probe　for　the　same　site　on　the　DNA　film,　it　would　displace　the　probe　from　the　DNA　to　decrease　the　ECL　signal.　The　interactions　of　DNA　with　three　pesticide　molecules,　quinalphos,　quinclorac　and　carbendazim,　were　studied.　From　the　displacement　curve,　the　values　of　binding　constant　K-b　of　three　pesticides　to　DNA　is　determined,　which　is　in　the　range　of　0.5x10(4)　to　2.3x10(4)M(1).