An　electrochemical　competition　method　was　used　to　study　the　interaction　of　carbaryl　with　natural　double-stranded　DNA　(ds-DNA).　Layer-by-layer　films　of　negatively　charged　natural　ds-DNA　and　polycationic　poly　(diallyldimethylammonium　chloride)　were　assembled　on　the　surface　of　a　glassy　carbon　electrode.　The　DNA　intercalator　[Ru(bpy)(2)(dppz)](2+)　(bpy　=　2,　2＇-bipyridine,　dppz　=　dipyrido　[3,　2-a:　2＇,3＇-c]　phenazine)　was　chosen　as　an　electrochemical　probe.　Tripropylamine　was　used　as　an　electron　donor　to　chemically　amplify　the　oxidation　current　of　the　probe.　In　order　to　examine　the　effects　of　substituting　group　on　the　binding　interaction　of　carbaryl　with　DNA,　the　interaction　of　naphthalene　or　alpha-naphthol　with　DNA　was　also　studied　by　square　wave　voltammetry　(SWV).　The　values　of　binding　constant　K　(b)　of　the　three　compounds　to　DNA　are　determined,　which　fall　in　the　range　of　(0.2　x　10(5))　to　(1.3　x　10(5))　M-1.　The　correlation　suggests　that　the　functional　groups　may　play　an　important　role　in　the　DNA/analyte　competition　binding　interaction.　We　demonstrated　that　it　is　conducive　to　the　combination　of　small　molecules　and　DNA　when　the　functional　groups　are　hydrophobic　and　have　the　lone-pair　electrons　as　the　electron　donor.　Furthermore,　UV-absorption　and　fluorescence　intensity　of　Ru-dppz　decreases　in　the　presence　of　carbaryl.　These　characteristics　strongly　support　the　intercalation　of　carbaryl　into　double-stranded　DNA.