Velocity and attenuation measurements were made in thin strips of rubber from 0.5 to 5 kc and from −5°C to 90°C to obtain the dynamic viscoelastic constants of butyl and GR‐S gum stocks. Above room temperature velocity and attenuation are higher in butyl gum than in GR‐S. In all cases, the velocity increases with decreasing temperature and increasing frequency. The attenuation shows a peak with temperature. For butyl the peaks are broad and occur at higher temperatures than for GR‐S. For both stocks an increase in frequency gives peaks which are higher and sharper, and shifted to higher temperatures. In some instances, there are indications of peaks in the attenuationversusfrequency at frequencies beyond our range of measurement. The behavior of the dynamic modulus in the temperature and frequency range studied is similar to that of the velocity. These results combined with low temperature static measurements and very low frequency dynamic measurements indicate a U‐shaped modulus‐temperature curve whose minimum broadens and shifts to higher temperatures with increasing frequency. This may be explained by a generalization of the kinetic theory of rubber elasticity, taking into account intra‐ and intermolecular forces, and considering time effects.