Two Vitis labrusca cultivars [Bordô (Ives), Concord] grafted to two rootstocks (1103 Paulsen, VR043-43) were combined in a randomized complete block experiment with a factorialized treatment arrangement in southern Brazil. Clusters were sampled over two seasons (2012, 2013) and analyzed for Brix, titratable acidity (TA) and pH, sucrose, glucose and fructose, as well as malvidin and cyanidin-3,5-diglucosides, quercetin and trans-resveratrol. Concord had the highest Brix and lowest TA in both years. Total sugars, glucose, and fructose were highest in Bordô/VR043-43 and Concord/1103 Paulsen. Total anthocyanins+quercetin were substantially higher in Bordô compared to Concord and were enhanced in both cultivars by VR043-43, while malvidin was increased in Bordô by VR043-43 as well. Cyanidin was detected in Concord only and was increased by VR043-43 in 2013. Quercetin and trans-resveratrol were detected in Bordô only; quercetin was highest in vines grafted to Paulsen 1103 and trans-resveratrol in those on VR043-43. The results suggest a strong rootstock influence on fruit composition of both cultivars-particularly quercetin and trans-resveratrol, which may have positive health implications in terms of antioxidant capacity.