We conducted removal experiments in open populations of Microtus ochrogaster and M. pennsylvanicus to test for potential interspecific competition between coexisting populations in bluegrass and tallgrass prairie in east-central IL, USA. Population densities of M. ochrogaster and M. pennsylvanicus in bluegrass were not suppressed by presence of the other species. In bluegrass, presence of the other species did not negatively influence monthly survival, persistence of young on the site, reproduction, or number of immigrants of either M. ochrogaster or M. pennsylvanicus. Although M. pennsylvanicus appeared to exert a strong suppressing effect on population densities of M. ochrogaster in tallgrass and limited the number of immigrants, survival, persistence of young, and proportion reproductively active female M. ochrogaster were not negatively affected by presence of M. pennsylvanicus. We conclude that interspecific competition did not play a major role in driving dynamics of coexisting populations of M. ochrogaster and M. pennsylvanicus in our study sites [Acta Zoologica Sinica 53 (5): 800–811, 2007].