Only a few studies have examined the effects of haying on species of small mammals in grasslands. We assessed this effect by trapping small mammals in autumn each year in 5 experimental (hayed) and 6 control (not hayed) sites in mixed grass prairie on the Smoky Hills Army National Guard Training Facility in Saline County, Kansas during 1998–2000. Only 1 species, the deer mouse (Peromyscus maniculatus), did not respond negatively to the change in habitat structure that resulted from haying. The remaining 8 species either occurred in lower numbers on the hayed sites or avoided them completely. Species richness was higher on the control sites (2.2 species per site) than on the experimental sites (0.87). Likewise, species diversity also tended to be higher on the control sites than on the experimental sites. Our results not only suggest the negative impact that summer-autumn haying has on small mammal species and communities in native and planted grasslands, but also has implications for the practice of mowing and baling of roadside ditches, which serve as refuges for many species of small mammals in landscapes dominated by croplands and rangelands.