A　highly　sensitive　electrochemical　sensor　is　described　for　the　determination　of　H2O2.　It　is　based　on　based　on　the　use　of　polyaniline　that　was　generated　in-situ　and　within　1min　on　a　glassy　carbon　electrode　(GCE)　with　the　aid　of　the　Fe(II)/H2O2　system.　Initially,　a　2-dimensional　composite　was　prepared　from　graphene　oxide　and　polyamidoamine　dendrimer　through　covalent　interaction.　It　was　employed　as　a　carrier　for　Fe(II)　ions.　Then,　the　nanocomposite　was　drop-coated　onto　the　surface　of　the　GCE.　When　exposed　to　H2O2,　the　Fe(II)　on　the　GCE　is　converted　to　Fe(III),　and　free　hydroxy　radicals　are　formed.　The　Fe(III)　ions　and　the　hydroxy　radicals　catalyze　the　oxidation　of　aniline　to　produce　electroactive　polyaniline　on　the　GCE.　The　resulting　sensor,　best　operated　at　a　working　potential　as　low　as　50mV　(vs.　SCE)　which　excludes　interference　by　dissolved　oxygen,　has　a　linear　response　in　the　500nM　to　2mM　H2O2　concentration　range,　and　the　detection　limit　is　180nM.　The　sensor　was　successfully　applied　to　the　determination　of　H2O2　in　spiked　milk　and　fetal　bovine　serum　samples.