This work was carried out for two smsons : 2004 and 2005 on twelve years old Thompson Seedless grapevines. Vines were differently trellised. three systems of trelllslng were applied at three locations in the vineyard; the first was the simple traditional telephone cane training system (in which vines had a high canopy density). the second was T trellis system (moderate density) and the third was double T trellis system (Low density). For measuring the canopy density a point quior thin long metal was used. This was inserted 50 times in the campy. then its going through gaps. leavm or clusters after which the data was recorded. Scores sheet was used for masurlng the canopy density through different steps then data were calculated. The results showed that number of clusterslvlne. cluster dimensions. cluster weight and T38 in berry juice were Increased at the low canopy density (double T system). Chlorophyll content was found to increase in this trmtrnent whereas leaf area was decreased. In the traditional cone system (high density}. cluster weight. cluster dimensions and total soluble solids in berry juice were decreased whereas acidity of the juice was increased. this was attributed to the high density canopy which did not allow light and aeration to penetrate within the canopy as to reach the interior parts of the foliage. This high density canopy needs special management with the aim of modifying microclimate of the vines.