The influence on fruit quality of peach x almond hybrids 'Adafuel', 'Adarcias' and 'GF 677', as rootstocks for 'Catherine' peach and 'Flavortop' nectarine were tested in two trials. The experiment was performed in the Ebro Valley, on a heavy and calcareous soil. To evaluate fruit quality, parameters such as fruit size, fruit weight, colour, firmness and some chemical properties of the fruit (acidity, pH and soluble solid concentration) were studied. In addition, the most important sugars found in fruit juice (sucrose, glucose, fructose and sorbitol) were analysed by High Performance Liquid Chromatography (HPLC). Significant differences in sugar concentrations, colour parameters, fruit weight and size were found among rootstocks. Nevertheless, no differences were shown for firmness. Preliminary results indicate that 'Adarcias' rootstock induces the highest soluble solid concentrations.