Piezoelectric transformers prepared using bulk PZT ceramic rings poled homogeneously along thickness were studied experimentally on the commercially available rings (PZT type APC841, d =20 mm, D = 50 mm and thickness 6 mm, aspect ratio d/D = 0.40) as well as analytically. Input and output parts were formed by the concentric ring electrodes. The fundamental and the first overtone were measured for the transformation ratio and efficiency. Ring transformer geometry shows the high transformation ratios (up to 108 under no-load condition for the first overtone) and efficiencies 91-99% for the properly designed electrode diameter. The optimum resistive load was relatively small within the range of 0.1 – 5kOhm. The optimum aspect ratio of electrode was found as d1/D = 0.70. The fundamental resonance frequency was found insensitive to the electrode diameter contrary to the first overtone. Analytical calculations are also used for the comparison of the mechanically free and clamped transformer. Mechanically clamped transformer generally shows higher resonance frequency.