Pb(Zn1/3Nb2/3)(0.20)(Zr0.50Ti0.50)(0.80)O-3 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 (k(p)) and dielectric loss (tan 8) are optimized for 0.5-wt%-MnO2-doped samples (k(p) = 0.60, tan delta = 0.2%) and the mechanical quality factor (Q(m)) is maximized for 1.0-wt%-MnO2-doped samples (Q(m) = 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.