Such aabiotic stresses like water stress are some of the most important threats to the production of agricultural crops. It is almost very rare to find a place with no stress where plants can reach their potential yield. A water stress of 17 percent decrease yield, due to its effect upon fruit setting is notable. Therefore, a study was conducted in Bushehr Agricultural Research Center (located in Borazjan) to determine the effect of irrigation timing and regime (in vegetative and reproductive stages) on yield and the quality of tomato. The experiment was carried out based upon a completely randomized block design of three replications during 2005-2006. The treatments of the study adopted were as follow: 1- complete irrigation during vegetative and reproductive stages (when soil moisture is depleted by 50% of the available water), 2- complete irrigation during vegetative stage and then water stress (when soil moisture is depleted by 65% of the AW) to the end of the reproductive stage, 3- complete irrigation during vegetative stage followed by water stress (when soil moisture is depleted by 80% of the AW) to the end of  reproductive stage, 4- stressed irrigation during vegetative stage (when soil moisture is depleted by 65% of the AW), then complete irrigation to the end of reproductive stage, 5- stressed irrigation during vegetative stage (when soil moisture is depleted by 80% of the AW) followed by complete irrigation to the end of reproductive stage. Such plant and fruit characteristics as yield, mean fruit weight, water use efficiency, pH, vitamin C content, dominant organic acidity (ascorbic acid) and TSS were assessed. Results indicated that the effect of irrigation treatments was significant on yield and water use efficiency (at 1% level), on total soluble solids and pH (at 5%), was not significant on vitamin C, mean fruit weight and active organic acidity. The treatment I₄ with a quaintly of 6336 m³ of irrigation water per ha per year was shown to be the most appropriate among all the treatments.