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To evaluate the effects of water stress at various phonological stages of peach fruit development on fruit characteristics, an experiment was conducted during a two year period at the experimental orchard of Agricultural College, Tehran University, in Karaj. A Split-plot design arranged in randomized completely block with four replications was used. Four cultivars (G. H. Hale, Red Haven, White Mashhad and Red-White Mashhad) were put in main plots and five water stress treatments (Water stress in stage I of fruit growth, Water stress in stage II, water stress in stage III, water stress in stage I plus stage II and control) in Sub-Plots. The results indicated that water stress at stage III of fruit growth significantly decreased the mean fruit weight, fruit size and fruit water content while total soluble solids (T. S. S) as well as fruit acidity were increased. Water stress at stage II of fruit growth (Pit hardening) increased fruit weight significantly (at 1% level) as compared with other treatments.