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Supplemental irrigation, which provide minimum amount of water under rainfed farming systems, improves the physiological characteristics and yield production of plants especially in arid and semi-arid regions. However, the amount and timing of supplemental irrigation are of utmost importance and challenging with the recent drought occurrences. A two-year field experiment was carried out to study the effect of different supplemental irrigation timings (March, April, May, June, March + April and no irrigation, denoted I-1,I-2,I-3,I-4,I-5 and I-6, respectively) on stomatal conductance (g(s)), photosynthesis rate (An) and leaf water potential of rainfed seedless Table grape, cv. Yaghooti. The I-1,I-2,I-3 and I-4 treatments received 5001 of water, while Is treatments received 10001 of water during the growth season, respectively. The significant maximum berry weight was obtained in the I-3 treatment in both years indicating the efficient use of applied water. Maximum and minimum values of An and gs were 12.10 mu mol m(-2) s(-1) and 0.133 mol m(-2) s(-1) in I-4 (in 114 days after first irrigation initiation), and 6.54 mu mol m(-2) s(-1) for 15 and 0.068 mol m(-2) s(-1) for I-1, respectively. It is concluded that supplemental irrigation during May (I-3) yielded more grape production, although it received less water compared to 15 treatments. (C) 2016 Elsevier B.V. All rights reserved.