In　this　paper,　the　shape　instabilities　of　Nb　in　in　situ　Cu-Nb　microcomposite　wires　after　exposed　to　different　annealing　treatments　have　been　analyzed　using　scanning　electron　microscopy　and　transmission　electron　microscopy　technologies.　The　results　suggest　that　the　thermal　stability　is　related　to　misorientation　among　the　adjacent　grains　at　the　triple　joint.　Most　of　the　triple　joints　are　composed　of　low-angle　grain　boundaries　in　Nb　ribbons　and　Cu-Nb　interfaces　of　(111)(Cu)//(011)(Nb).　These　triple　joints　provide　dragging　force　to　interface　motion　so　that　neither　the　grains　nor　the　interface　boundaries　show　substantial　changes　below　500　degrees　C.　Above　500　degrees　C,　the　Nb　ribbons　start　to　dissociate　at　the　triple　joints　within　Nb　phase　due　to　the　stored　energy　by　misorientation/distortion　in　Nb.　Grooves　and　pits　formed　at　these　regions　tend　to　promote　the　spheroidization　of　the　Nb　phase.　Such　results　may　enrich　the　studies　on　the　microstructure　evolution　of　Cu-based　microcomposite.