The effect of grain size distribution on the measured acoustic nonlinearity of polycrystalline engineering materials is investigated. Results are provided for two austenitic stainless steel materials with comparable mean grain sizes and distinct distribution widths assuming equiaxed grains and random crystallographic orientation. The distribution width is shown to influence the nonlinearity parameter considerably. On the material with a wider distribution, a reduced nonlinearity was noted, and comparable trends were also noted for different frequencies investigated. The results predict that the existing models that account for only the mean grain size when characterizing material degradations need to be modified more comprehensively to include the role of grain size distribution. © 2020 Author(s).