Technical Abstract: Seed dormancy is a naturally important biological process which can affect planting, germinating, and harvesting in agricultural production. Variability in seed dormancy within the U.S. peanut mini-core collection had not been determined. Freshly harvested seeds in the same field from 103 accessions were tested for germination with two treatments (H2O only or 10 mM ethephon). The number of seeds that germinated or died was recorded. Significant variability in seed dormancy was observed among accessions and botanical varieties. In comparison with the H2O treatment, ethephon significantly promoted dormancy release, but the level of dormancy release was genotype dependent. The interaction effect (genotype x treatment) on seed dormancy release was also determined. Seed dormancy among four botanical varieties was compared. The botanical variety of hypogaea was more dormant than the other three botanical varieties evaluated. However, significant variability was also identified within botanical varieties. The accessions identified with greater dormancy within the same botanical variety would be useful in breeding programs to prevent preharvest sprouting. There are six botanical varieties in cultivated peanuts, but only four botanical varieties were included in the U.S. peanut min-core collection. The variability in seed dormancy for the other two botanical varieties needs to be investigated in future studies.