The resonance spectrum of any specimen is dependent on its symmetry, density, geometry, elastic properties, and the boundary conditions. By using specimens with simple known geometry and models including speci-men symmetry, resonance ultrasound spectrosopy can determine the full elastic stiffness tensor to great precision with one measurement. This measurement is fast, taking less than a minute with state-of-the-art instrumentation, making it appropriate for measuring properties as a function of temperature. Parts per million changes in specimen density, geometry, elastic moduli, temperature, and boundary conditions can be detected in carbon fiber reinforced epoxy composite materials with resonance ultrasound spectroscopy. It is important to know the mechanical properties of carbon fiber reinforced epoxy composite materials at low temperatures for underwater, space, and polar applications. The amplitude/frequency resonance spectra of four different lay-ups of AS4/3501-6 carbon fiber reinforced epoxy composite have been measured at 1 (degrees)C intervals from -177 (degrees)C to 25 (degrees)C. The spectra indicate increasing stiffness and decreasing damping with decreasing temperature.