Peanut (Arachis hypogaea L.) is the secondmost important legume crop in the United States. A limitation to increased peanut productivity is that peanut improvement is hampered by relatively low genetic variability in the germplasm commonly used by breeding programs. To facilitate accessibility to diverse germplasm sources for breeding applications, a core subset of the USDA peanut germplasm was previously established that later was further refined and developed into a mini core collection consisting of 112 accessions. This report details an extensive characterization of genetic diversity and relationships in the U.S. peanut mini core using microsatellite or simple sequence repeat (SSR) markers. Seventy-two peanut accessions from the U.S. peanut mini core were genotyped with 73 SSR markers; all but six produced reliable, polymorphic bands. Moderate levels of genetic variation were found with genetic distances (D) values among accessions ranging from 0.088 to 0.254. Distinct groupings of the accessions based on subspecies classification and on botanical (market) type groupings were established. Twelve of the markers, mapped previously to the A genome, were found to be sufficient to identify both subspecies and botanical types and gave a clustering pattern very similar to the entire 67 SSR marker set. The genetic variation observed within U.S. peanut mini core can be utilized for selection of diverse parents for breeding and development of mapping populations.