This　paper　presents　an　investigation　on　the　active　vibration　control　of　flexible　linkage　mechanisms　featuring　piezoceramic　actuators　and　strain　gauge　sensors.　The　dynamic　equation　of　the　macroscopically　smart　mechanism　is　decoupled　by　means　of　the　complex　mode　theory.　The　state-space　expression　of　the　controlled　system　is　developed,　which　includes　the　system　noise　and　the　observation　noise.　Moreover,　a　discrete　linear　quadratic　Gaussian　(LQG)　state　feedback　controller　and　a　discrete　Kalman　filter　are　designed　separately.　Finally,　the　proposed　method　is　applied　to　the　on-line　vibration　control　of　a　macroscopically　smart　mechanism.　The　experimental　results　reveal　that　the　strain　amplitude　of　the　flexible　link　is　suppressed　by　80　%　and　the　dynamic　performance　of　mechanism　has　been　ameliorated　significantly.