Pb(Zn1/3Nb2/3　0.20(Zr0.50Ti0.50　0.80O3　ceramics　of　pure　perovskite　structure　were　prepared　by　the　two-stage　method　with　the　addition　of　0-3.0　wt%　MnO2　and　their　piezoelectric　properties　were　investigated　systematically.　The　MnO2　addition　influences　in　a　pronounced　way　both　the　crystal　structure　and　the　microstructure　of　the　materials.　The　materials　are　transformed　from　the　tetragonal　to　the　rhombohedral　structure,　and　the　grain　size　is　enhanced　when　manganese　cations　are　added.　The　distortion　of　crystal　structure　for　samples　with　MnO2　addition　can　be　explained　by　the　Jahn-Teller　effect.　The　values　of　electromechanical　coupling　factor　(kp)　and　dielectric　loss　(tan　δ)　are　optimized　for　0.5-wt%-MnO2-doped　samples　(kp　=　0.60,　tan　δ　=　0.2%)　and　the　mechanical　quality　factor　(Qm)　is　maximized　for　1.0-wt%-MnO2-doped　samples　(Qm　=　1041),　which　suggests　that　oxygen　vacancies　formed　by　substituting　Mn3+　and　Mn2+　ions　for　B-site　ions　(e.g.,　Ti4+　and　Zr4+　ions)　in　the　perovskite　structure　partially　inhibited　polarization　reversal　in　the　ferroelectrics.　The　ceramics　with　0.50-1.0　wt%　MnO2　addition　show　great　promise　as　practical　materials　for　piezoelectric　applications.