This　paper　proposed　a　novel　negative　stiffness　damped　outrigger　with　damping　amplification　(NSDO-DA)　through　a　smart　combination　of　an　L-shape　lever,　a　precompressed　disc　spring　brace　(DSB),　and　a　viscous　damper.　A　theoretical　model　of　the　NSDO-DA　considering　nonlinear　adaptive　negative　stiffness,　damping　amplification　of　nonlinear　viscous　dampers,　and　frictions　were　established.　Cyclic　tests　of　disc　spring　pairs　and　DSB　were　presented　to　verify　the　feasibility　of　using　DSB　as　the　precompression　component　of　the　NSDO-DA.　Subsequently,　large-scale　dynamic　tests　of　five　different　outrigger　systems　were　conducted　involving　(i)　conventional　damped　outrigger　(CDO),　(ii)　amplified　damped　outrigger　(ADO),　(iii)　purely　negative　stiffness　mechanism,　(iv)　negative　stiffness　damped　outrigger　(NSDO),　and　(v)　NSDO-DA.　Then,　discussions　on　the　dynamic　test　results　and　validations　of　the　NSDO-DA　model　were　provided.　The　major　contributions　of　this　paper　are　the　proposal　of　the　NSDO-DA　and　the　experimental　validation　of　its　two　special　features:　(i)　producing　negative　stiffness　force　in　the　parallel　direction　of　the　precompression　force　rather　than　in　the　perpendicular　direction,　making　the　physical　configuration　more　concise　and　condensed　for　outrigger　application;　(ii)　sharing　the　amplification　mechanism　of　the　L-shape　lever　for　both　the　viscous　damper　and　the　negative　stiffness　mechanism,　leading　to　an　additional　damping　amplification　mechanism　for　the　damper.　Moreover,　the　adaptive　stiffness　behavior　and　the　frequency-independent　feature　of　the　proposed　negative　stiffness　mechanism　were　successfully　validated　by　the　dynamic　tests.