The Smith-Birchak model for magnetoelastic damping was successfully applied to model the damping observed in an antiferromagnetic Cu-48Mn-1.5Al (wt pct) alloy. Antiferromagnetic domains were developed by solution treatment at 820 ‡C and subsequent aging at 400 ‡C for 4, 10, and 16 hours. Damping capacity and dynamic elastic modulus were measured as a function of strain amplitude and temperature. A maximum in the strain-amplitude-dependent damping was obtained for the 4-hour-aged sample for which a magnetostriction constant, λ, equal to 4.65 × 10 -4, was derived. An exact fit for the Smith-Birchak model was obtained at low strains, whereas the model predicted lower damping than was observed for strains greater than 1.1 × 10 -3. This discrepancy was attributed to an additional damping mechanism at high strain amplitudes, i.e., dislocation damping. A magnetostriction constant equal to 3.23 × 10 -4 was also calculated based upon the Néel temperature and the observed microstructure. © 1995 The Minerals, Metals & Material Society.