Nitrogenated diamond-like carbon (a-C:N) thin films on Si(100) were deposited by radio frequency magnetron reactive sputtering. Using ZnO piezoelectric thin films, the surface acoustic wave (SAW) propagation properties of a-C:N thin films on Si(100) have been experimentally investigated using bidirectional interdigital transducers between ZnO and a-C:N/Si(100). A generalized SAW mode with velocities between 5000 and 7000 m/s were observed. A high velocity pseudo-SAW mode was also observed and identified with simulated data, of which the velocity was 13 850 m/s. We calculated the film elastic constants from the phase velocities in the layered structure. The calculated constants for a-C:N thin films on Si were c(11)=392.1 and c(44)=185.7 GPa.