Technical Abstract: Determining the cultivar identity of blackberry fruit may be problematic when the parent plant is not available for examination. The ability to correctly identify commercial cultivars is important to the industry. Less desirable cultivars may be mistaken or substituted for more desirable ones, resulting in mislabeled products or economic losses. Often processers are interested in distinguishing a highly popular cultivar from other commercially grown blackberries with similar fruit characteristics. The objective of this study was to develop an effective way to distinguish blackberry cultivars using seed morphology. Seed of 17 commercially important blackberry cultivars collected from the US Department of Agriculture (USDA), Agricultural Research Service (ARS), National Clonal Germplasm Repository (NCGR) and Horticultural Crops Research Laboratory (HCRL) were examined with light and scanning electron microscopy. One key characteristic is the shape of the raphe: straight, concave or convex. Seed shape, color, size and seed-coat sculpturing further distinguish the cultivars. Although scanning electron microscopy showed the seed coat sculpturing in greater detail, it was not required to differentiate these cultivars.