The colonial bentgrass species (Agrostis capillaris L.) is a potential source for genetic improvement of resistance to environmental stress and disease for other bentgrass species (Agrostis spp.). To conserve and study the existing genetic resources of colonial bentgrass for various breeding use, genetic diversity in the colonial bentgrass species was investigated by amplified fragment length polymorphism (AFLP) markers. Included in this study were twenty-two accessions from USDA germplasm collected from 11 countries, fourteen accessions from north Spain, and three commercial cultivars. Ten EcoRI/MseI and six PstI/MseI AFLP primer combinations produced 181 and 128 informative polymorphic bands, respectively. Cluster analysis of genetic similarity estimates revealed a high level of diversity in colonial bentgrass species with averages of 0.51 (EcoRI/MseI) and 0.63 (PstI/MseI). Greater genetic diversity was detected by EcoRI/MseI AFLP primer combinations. A low but significant positive correlation (r=0.44, p=0.0099) between the two Jaccard's similarity matrices was obtained by the Mantel test. The commercial cultivars showed a narrow genetic background. The assessment of genetic diversity among colonial bentgrass accessions provided the necessary information for utilization of the colonial bentgrass germplasm in turfgrass cultivar improvement.