Accurate in situ evaluation of the changes in material properties of an asphalt surface layer due to fatigue loading and rest periods is important for a better understanding of fatigue mechanisms of asphalt concrete in the field and therefore more realistic prediction of the fatigue life of asphalt pavements. A nondestructive technique based on the stress wave propagation method is presented as a means of measuring the changes in the “apparent” modulus of an asphalt surface layer due to fatigue damage growth and healing during rest periods. The method was applied to four asphalt pavements in the FHWA Turner Fairbank Highway Research Center that were loaded by the Accelerated Loading Facility to induce fatigue damage. The dispersion analysis is performed using the Short Kernel Method on the wave transients measured at different loading cycles and after rest periods. The results indicate that (a) the test and analysis technique used provides a sensitive means of evaluating the changes in asphalt surface layer properties during fatigue loads and rest periods, (b) the elastic modulus of the asphalt layer decreases as the number of loading cycles increases in an S-shape decaying curve, and (c) the effective modulus of the asphalt layer increases because of the introduction of rest between loading cycles.