Low water availability has increased the use of regulated deficit irrigation strategies in fruit orchards.However, these water restrictions may have implications on fruit growth and quality. The current paperassesses the suitability of an existing fruit tree model (QualiTree) for describing the effects of water stresson peach fruit growth and quality. The model was parameterised and calibrated for a mid-late maturingpeach cultivar (‘Catherine’). Mean and variability over time of fruit and vegetative growth were consistentwith observed data on trees submitted to full irrigation or to regulated deficit irrigation. The relative rootmean square errors of the model for growth ranged between 0.09 and 0.31.Sugar contents in fruit flesh were fairly well simulated, except for sucrose, which was overestimated.The relative root mean square errors of the model ranged from 0.01 to 0.40 for fructose; from 0.04 to0.05 for glucose; from 0.21 to 0.41 for sucrose and from 0.09 to 0.28 for sorbitol. Water stress reducedleafy shoot growth up to 23% and fruit final size up to 49% when compared to the well-watered control.However, sugar contents in the flesh increased with water stress, up to 70% in the case of glucose. Sim-ulations showed that a severe water stress during stage III of fruit development decreased fruit sizes by22%, when compared to the control, whereas it enhanced sugar accumulation in the fruit flesh, up to 70%in the case of glucose and fructose. Therefore, these simulations showed that QualiTree might be usefulin the design of innovative horticultural practices.