Aims: in order to investigate the effect of vine training system on grape phenolic composition, a divided canopy system (Lyre) and a vertical shoot positioned trellis with two different pruning systems (Royat and Guyot) were applied in a commercial vineyard of cv. Xinomavro (Vitis vinifera L.). The quality of the produced grapes was determined with respect to three analytical parameters: anthocyanin content, tannin composition and proanthocyanidin structure. Methods and results: monomeric anthocyanins, flavan-3-ol monomers and oligomers, tannin mean degree of polymerization (mDP), galloylation percentage (%G), and extension and terminal subunit structure were determined in seeds and skins by HPLC and LC/MS. Total phenolics, anthocyanin content, tannin concentration and antioxidant activity were measured in whole berries. Grapes and wines of the Lyre system were characterized by increased concentration of total and individual anthocyanins and total phenols. Individual flavan-3-ol monomers and oligomers were highest in Royat grape skins and Guyot seeds. Concerning proanthocyanidin structure, Royat grapes had significantly higher mDP and lower %G in skin and seed polymeric tannin fractions, compared to the other two systems, possibly leading to a lower grape astringency potential. Conclusion: training system may affect grape anthocyanin concentration, total flavan-3-ol content as well as skin and seed proanthocyanidin structure (mDP, %G, extension and terminal subunits). Significance and impact of the study: The results of the present study could be of high importance to both grape growers and winemakers. Xinomavro grapes are rather poor in anthocyanins while being characterized by dry and astringent tannins. By adopting Lyre as a training system, higher anthocyanin contents could be achieved in grapes, resulting in wines with more attractive colour when adopting a longer pre-fermentation skin contact process. On the contrary, grapes of the Royat system might be more appropriate to produce full-bodied wines with higher ageing potential, due to their more appropriate tannin structure, by using longer maceration periods.< Réduire