Plasmonic　hollow　fibers　are　fabricated　by　coating　silver-/　gold-alloyed　nanoparticles　(Ag-Au-ANPs)　onto　the　inner　walls　of　hollow　fibers.　In　this　Letter,　the　Ag-Au-ANPs　were　synthesized　chemically　and　dissolved　in　acetone　to　prepare　a　colloidal　solution,　flowed　subsequently　through　the　hollow　fiber　multiple　times　so　that　a　thin　layer　of　colloidal　Ag-Au-ANPs　was　produced　on　the　inner　wall.　Annealing　at　400　degrees　C　enabled　melting/aggregation　of　the　metallic　nanoparticles　and　consequent　formation　of　closely　arranged　plasmonic　nanostructures　fixed　solidly　on　the　inner　wall.　A　surface-enhanced　Raman　scattering　(SERS)　mechanism　was　thus　established　for　the　liquids　flowing　through　the　hollows.　The　SERS　measurements　show　an　enhancement　factor　＞104　for　such　plasmonic　hollow　fibers　in　the　direct　detection　of　R6G/ethanol　solutions.　Confinement　of　the　excitation　laser　energy　inside　the　hollow　space　represents　an　additional　contribution　to　the　enhancement　mechanism.　This　is　a　promising　design　for　the　direct　on-site　SERS　detection　of　molecules　in　flowing　liquids　with　low　concentrations.　(C)　2021　Optical　Society　of　America