Diamond and AlN are, respectively, the nonpiezoelectric and the piezoelectric materials showing the highest acoustic velocities. Consequently, pseudo-surface-acoustic waves (PSAWs) in AlN/diamond structures exhibit the highest surface wave velocities among all known layered structures. Phase velocity dispersion curves and attenuation for PSAW propagating along this structure have been calculated for different electrical boundary conditions. An experimental delay line, designed to operate at low PSAW attenuation conditions, as predicted by theoretical results, has been implemented and tested. A good accordance between experimental results and theoretical predictions was found. It is expected that devices based on PSAW propagation in AlN/diamond structures are suitable to operate at frequencies several times higher than those of available devices, at a given linewidth resolution limit in the transducers technology.