The design and performance of a compact apparatus for the characterization of internal friction in simple shear at elevated temperature (≤1400 °C) and low frequencies (≤1 Hz) are described. High-temperature components are fabricated from a refractory molybdenum alloy that is straightforwardly machined. The apparatus has demonstrated, at high temperature, a torque resolution of 2×10-5 N m and an angular displacement resolution of 4×10-6 rad; for the specimen size we employ, these limits provide a shear stress and strain resolution of 2 kPa and 5×10-7, respectively. The apparatus, while applicable to dynamic and static mechanical analyses of any engineering material, was developed for the characterization of internal friction (attenuation) in synthetic silicate aggregates representative of Earth’s upper mantle; we discuss the constraints inherent in the required tests, as they affect apparatus design (including materials selection) and experimental protocol. Static and dynamic data at 1250 °C for a polycrystalline aggregate of ferromagnesian olivine of controlled, uniform (∼3 μm) grain size are presented and discussed.© 1998 American Institute of Physics.