The characteristics of surface acoustic waves (SAWs) on proton-exchanged (PE) and annealed proton-exchanged (APE) Z-cut Y-propagated LiNbO3 waveguides using pure pyrophosphoric acid are investigated and compared. The distribution of hydrogen in the PE samples measured by secondary-ion mass spectrometry (SIMS) shows a step-like profile with the diffusion constant D0 and the activation energy Q of about 9×107 µ m2/ h and 82.18 kJ/mol, respectively. The velocity (V p) of SAW on PE samples decreases with the increase of kd, where k is 2π/λ and d is the waveguide depth, and almost exhibits an exponential decay. However, post-annealing will result in a restoration of the decreased velocity and an improvement of the SAW insertion loss (IL). On the other hand, the electromechanical coupling coefficient (K2) almost decreases with the increase of kd and shows greater sample-to-sample discrepancy.