Spotted knapweed (Centaurea stoebe L. ssp. micranthos [Gugler] Hayek) is an exotic plant that displaces native vegetation leading to altered plant and animal communities. We compared small mammal abundance and diversity in areas with, and without, spotted knapweed in Grand Sable Dunes, Michigan, to determine whether presence of this plant affected the small mammal community. We live trapped small mammals in June and August 2003 in six plots in native dune vegetation and in six plots in areas with spotted knapweed and native dune vegetation. Mean number of captures per trap of mice in spotted knapweed plots ( = 0.50 ± 0.31) was nearly double that in native plot ( = 0.27 ± 0.19; F_1,20 = 18.251, P < 0.001). Amount of total vegetative cover in spotted knapweed plots ( = 71 ± 12% SD) was almost twice that in native plots ( = 37 ± 11%). Mean number of captures per trap was positively related to percent cover (F_1,20 = 5.239, P = 0.033). Mice are seed and insect predators, seed and spore dispersers, and serve as prey for numerous species. Thus, the positive response by mice to the spotted knapweed invasion may have caused additional changes to this community.