In grapevine (Vitis vinifera L.), seedlessness is classified into two distinct types: parthenocarpy and stenospermocarpy. Stenospermocarpy (seedlessness due to seed abortion) in grapevine is an agronomically valuable trait which is completely hereditary and not influenced by various environmental factors. Many hypotheses have been proposed for stenospermocarpy. However, the molecular mechanisms underlying development or abortion of the seed are still poorly understood. To identify genes involved in seed development or abortion in grape, we carried out Sequence-Related Amplified Polymorphism (SRAP)-cDNA analysis of grape seed development, comparing the seedless cultivar Youngle with the seeded cultivar Pinot noir. We identified VviABCG20, which encodes a putative ATP binding cassette G transporter, as a gene more highly expressed in ‘Pinot noir’. VviABCG20 is highly expressed in root, floral bud, seed and the expression level of VviABCG20 in all of five seeded grapevine cultivars tested was generally higher than that observed in seedless cultivars. Sequencing of VviABCG20 cDNAs from six stenospermocarpic seedless and seven seeded genotypes revealed that the seed-associated expression pattern of VviABCG20 was unrelated to sequence difference within the transcribed regions. Suppression of the tomato homolog of VviABCG20 in developing tomato fruit led to reduction in seed numbers, suggesting that LeABCG20 plays an essential role in seed development. Our experiments suggest that regulation of VviABCG20 is associated with seed development, and provide a new insight into the mechanism underlying seed abortion in stenospermocarpic grapes.