The　chatter　vibration　in　high-speed　machining　mostly　originates　from　the　flexible　connection　of　spindle　and　toolholder.　Accurate　identification　of　spindle-toolholder　joint　is　crucial　to　predict　machining　stability　of　spindle　system.　This　paper　presents　an　enhanced　stiffness　identification　method　for　the　spindle-toolholder　joint,　in　which　the　rotational　degree　of　freedom　(RDOF)　is　included.　RDOF　frequency　response　functions　(FRFs)　are　formulated　based　on　finite　difference　technique　to　construct　a　completed　spatial　FRF　for　the　joint,　where　the　measured　data　can　be　obtained　from　the　piezoelectric　acceleration　sensors.　In　order　to　depress　the　influence　of　＂modal　truncation＂　and　measurement　noises,　residual　compensation　theory　is　introduced　to　regenerate　the　RDOF　FRF.　Experiments　are　conducted　to　demonstrate　the　efficiency　of　the　proposed　model　in　stiffness　identification　of　spindle-toolholder　joint,　and　the　accuracy　is　significantly　improved　compared　to　the　traditional　model.