This　paper　presents　an　experimental　verification　of　a　method　of　evaluating　local　damage　in　steel　beam-column　connections　using　modal　vibratory　characteristics　under　ambient　vibrations.　First,　a　unique　testing　method　is　proposed　to　provide　a　vibration-test　environment　which　enables　measurements　of　modal　vibration　characteristics　of　steel　beam-column　connection　as　damage　proceeds.　In　the　testing　method,　a　specimen　of　structural　component　is　installed　in　a　resonance　frame　that　supports　large　fictitious　mass　and　the　resonance　frequency　of　the　entire　system　is　set　as　the　natural　frequency　of　a　mid-rise　steel　building.　The　specimen　is　damaged　quasi-statically,　and　resonance　vibration　tests　are　conducted　with　a　modal　shaker.　The　proposed　method　enables　evaluation　of　realistic　damage　in　structural　components　without　constructing　a　large　specimen　of　an　entire　structural　system.　The　transition　of　the　neutral　axis　and　the　reduction　of　the　root　mean　square　(RMS)　of　dynamic　strain　response　are　tracked　in　order　to　quantify　damage　in　floor　slabs　and　steel　beams,　respectively.　Two　specimens　of　steel　beam-column　connection　with　or　without　floor　slab　were　tested　to　investigate　sensitivity　of　the　damage-related　features　to　loss　of　floor　composite　action　and　fractures　in　steel　beams.　In　the　end,　by　updating　numerical　models　of　the　specimens　using　the　identified　damage-related　features,　seismic　capacities　of　damaged　specimens　were　estimated.