A bolt-clamped ultrasonic viscometer was designed and fabricated using a pair of ring-shaped piezoelectric ceramic resonators. For its compactness and low operation frequencies, simulation of piezoelectric resonators was carried out using an ATILA program. Ring-shaped resonators using 0.05Pb(Mn1/3Sb2/3)O3-0.95Pb(Zr0.475Ti0.525)O3 ceramics were prepared by a conventional ceramic processing, which were then clamped with a pair of metal caps. The fabricated sensor module with a small volume of less than 1 cm3 and an operation frequency as low as 26.5 kHz showed a good relationship between its quality factor and the viscosity of oil.