When　the　characteristics　of　the　main　structure　are　changed,　tuned　mass　damper　(TMD)　is　easy　to　meet　off-tuning　problem.　The　object　of　this　study　is　to　develop　a　TMD　with　shape　memory　alloy　(SMA)　to　reduce　the　vibration　caused　by　off-tuning　under　seismic　excitations.　By　materials　characterisation　of　SMA,　when　the　working　temperature　rises　from　-40　degrees　C　to　65　degrees　C,　the　stiffness　increases　and　the　equivalent　damping　ratio　drops.　The　SMAbased　TMD　was　installed　on　a　steel　frame　and　tested　under　earthquake　loading.　The　results　show　the　SMA-based　TMD　is　able　to　reduce　the　seismic　response　in　the　range　of　34.09-47.77%　at　the　tuned　condition.　However,　by　changing　the　main　structural　mass,　the　TMD　was　easy　to　be　off-tuned.　To　retune　the　TMD,　the　SMA　was　heated　and　cooled　for　the　TMD　to　resonate　with　the　natural　frequency　of　the　main　structure.　When　the　SMA　is　cooled,　the　peak　and　RMS　accelerations　can　be　effectively　reduced　by　up　to　23.98%　and　35.51%,　respectively.　It　was　found　that　the　SMA-based　TMD　performs　well　if　the　frequency　change　of　the　main　structure　is　in　the　same　order.　But　when　the　temperature　of　SMA　is　increased　higher　than　19　degrees　C,　the　damping　ratio　of　SMA　decreases,　which　causes　a　less　effectiveness　in　reducing　the　vibration.　In　the　future,　the　combinations　of　multiple　SMA　bars　in　TMD　should　be　studied,　and　the　applications　of　SMAs　with　higher　phase　transformation　temperature　can　be　investigated　to　improve　the　sensitivity　while　heating.