Mechanical　properties　of　electroplating　copper　(Cu)　filled　in　the　through　silicon　vias　(TSVs)　are　critically　important　in　the　reliability　assessment　of　TSV　packages.　In　order　to　obtain　its　mechanical　properties,　such　as　Young＇s　modulus,　hardness,　and　stress-strain　relationship,　wafers　with　TSVs　are　fabricated　by　a　typical　manufacturing　process,　and　then　nanoindentation　tests　are　conducted　to　extract　Young＇s　modulus　and　the　hardness　of　TSV-Cu.　The　3-D　finite-element　method　simulations　of　the　nanoindentation　tests　are　conducted　to　determine　the　power　law　stress-strain　relationship　of　the　TSV-Cu　by　an　iteration　algorithm　in　which　the　simulated　maximum　nanoindentation　force　is　compared　with　that　by　tests.　Finally,　Young＇s　modulus　and　the　hardness　of　the　TSV-Cu　obtained　are　155.47　and　2.47　GPa,　respectively.　In　addition,　the　power　law　stress-strain　relationship　of　the　TSV-Cu　is　presented,　in　which　the　strain　hardening　exponent　is　0.4892　and　the　yield　stress　is　47.91　MPa.　This　constitutive　relationship　can　be　used　to　compute　stress,　strain,　and　deformation　in　TSV　packages.