Surface-enhanced　Raman　spectroscopy　(SERS)　has　been　widely　investigated　and　employed　as　a　powerful　optical　analytical　technique　providing　fingerprint　vibrational　information　of　molecules　with　high　sensitivity　and　resolution.　In　addition　to　metallic　nanostructure,　dielectric　micro-/nano-structures　with　extraordinary　optical　manipulation　properties　have　demonstrated　capability　in　enhanced　Raman　scattering　with　ultralow　energy　losses.　Here　we　report　a　facile　cascaded　structure　composed　of　a　large　microsphere　(LMS)　and　a　small　microsphere　array　with　Ag　nanoparticles　as　a　novel　hybrid　SERS　substrate,　for　the　first　time.　The　cascaded　microsphere-coupled　SERS　substrate　provides　a　platform　to　increase　the　molecular　concentration,　boost　the　intensity　of　localized　excitation　light,　and　direct　the　far-field　emission,　for　giant　Raman　enhancement.　It　demonstrates　the　maximum　enhancement　factor　of　Raman　intensity　greater　than　10(8)　for　the　limit　of　detection　down　to　10(-11)　M　of　4-nitrothiphenol　molecules　in　aqueous　solution.　The　present　work　inspires　a　novel　strategy　to　fabricate　cascaded　dielectric/metallic　micro-/nano-structures　superior　to　traditional　SERS　substrates　towards　practical　applications　in　cost-effective　and　ultrahigh-sensitive　trace-detection.