The　atom-bond　connectivity　(ABC)　index　provides　a　good　model　for　the　stability　of　linear　and　branched　alkanes　as　well　as　the　strain　energy　of　cycloalkanes,　which　is　defined　as　ABC(G),　where　d　u　denotes　the　degree　of　a　vertex　u　in　G.　A　chemical　graph　is　a　graph　in　which　no　vertex　has　degree　greater　than　4.　In　this　paper,　we　obtain　the　sharp　upper　and　lower　bounds　on　ABC　index　of　chemical　bicyclic　graphs.　©　2012　Editorial　Committee　of　Applied　Mathematics-A　Journal　of　Chinese　Universities　and　Springer-Verlag　Berlin　Heidelberg.