Prairie cordgrass and switchgrass are strong candidates for biomass production on wet marginal land in the northern Great Plains. In natural ecosystems, such as the tallgrass prairie, cordgrass is better adapted to water-logged soils than switchgrass. However, both species are suitable for production of biomass in areas where annual cropping is unpredictable due to high water table or flooding. The objective of this study was to compare biomass production of switchgrass to prairie cordgrass on two soils in eastern South Dakota that were frequently too wet to plant to annual grain crops in the spring.  Biomass of prairie cordgrass was greater than three times that of switchgrass when harvested at physiological maturity. Tiller density was comparable for the two species, whereas tiller mass was greater for prairie cordgrass. Prairie cordgrass was better adapted  than switchgrass for sustainable biomass production on wet soils in the northern Great Plains.