Acoustic phase velocity surfaces and ray directions in paratellurite,TeO2, have been calculated. Characteristic features of the wave propagation in this highly anisotropic medium have been optically confirmed using the shadow method and Schaefer‐Bergmann diffraction technique. A small misalignment of the wave normal direction has been found to degrade seriously the performance characteristics of acoustic or acousto‐optical devices composed of a highly anisotropic medium such asTeO2. The existence of the transverse mode with a zero temperature coefficient of velocity has been also confirmed by the present calculation and experiment.