This　paper　presents　a　three-step　method　for　the　stiffness　identification　of　inter-story　shearing　structures　under　ambient　excitation.　The　transition　from　structural　random　response　to　deterministic　response　is　realized　by　the　natural　excitation　technique　(NExT).　The　parameter-decoupled　free　vibration　equation　of　inter-story　shearing　structures　is　deduced,　which　can　simplify　the　procedure　of　identification　and　reduce　the　amount　of　calculation.　Through　the　effective　combination　of　the　NExT,　the　parameter-decoupled　method,　and　the　extended　Kalman　filter　(EKF)　algorithm,　a　good　scheme　is　presented　for　stiffness　identification　of　inter-story　shearing　structures　under　ambient　excitation.　Using　inter-story　shearing　structures　with　six-degree-of-freedom　and　ten-degree-of-freedom　as　examples,　the　scheme　is　tested　by　numerical　simulation　and　experiment.　The　result　shows　that　the　maximum　of　identification　error　is　7.82%,　and　it　can　reach　the　requirement　of　engineering　application　basically.　©　2009　Tsinghua　University　Press.