The　Megami　Bridge,　with　a　main　span　of　480　in,　is　the　6th　longest　cable-stayed　bridge　in　Japan.　A　comparison　of　experimental　and　analytical　modal　analysis　is　performed　to　determine　the　dynamic　characteristic　of　this　bridge.　The　ambient　vibration　test　is　carried　out　using　very　few　accelerometers.　Parameter　identification　is　carried　out　using　the　stochastic　subspace-based　identification　(SSI)　method　in　the　time-domain　as　proposed　by　Katayama.　The　SSI　method　used　in　this　paper　can　be　used　for　estimating　the　modal　properties　of　a　long　span　cable-stayed　bridge　by　comparing　with　the　maximum　entropy　method　(MEM).　Furthermore,　the　effectiveness　of　the　tuned　mass　dampers　(TMDs)　used　in　the　bridge　is　evaluated　through　a　human　excitation　test.　Logarithmic　damping　is　about　0.030　when　the　TMD　is　activated,　a　little　higher　than　the　design　value　0.026,　so　proving　that　the　TMDs　are　effective.　Finally,　the　analytical　eigenvalues　obtained　from　finite　element　analysis　agree　well　with　the　experimental　values,　thus　verifying　the　analytical　model.