Two field experiments were carried out at the Experimental Farm, Faculty of Agriculture, Minufiya Univ., at Shebin El-kom to study the effect of three irrigation regimes, i.e. 40, 55 and 70 % available soil moisture depletion (ASMD) on growth, seed yield and its components as well as seed quality of four sunflower cultivars namely Pioneer-6480, Euroflor, Elya and Miak during 1996 and 1997 seasons. The treatments were arranged in split-plot design with four replicates where the irrigation treatments occupied the main plots and the tested sunflower cultivars were assigned in the sub-plots. The most important results are summarized as follows:   1-Sunflower plants grown under water stress (40% ASMD) showed significantly higher in plant height, number of green leaves/plant, stem diameter, leaf area/plant, total dry matter/plant, LAI and SLA at all sampling dates which were 45, 60 and 75 days after sowing, and RGR, NAR and CGR values at the period of 45-60 days. On the contrary, exposed plants to 40% ASMD led to significantly lower in RGR, NAR and CGR values at the period of 60-75 days compared to 55% and 70% ASMD treatments in both seasons. Also, sunflower plants exposed to water stress at 40% ASMD gave the highest mean values for seed yield/plot and its components and seed oil percentage in both seasons. A gradual depression in seed yield/plot and its component mean values, parallel to the decrease in amount of available water in the soil was detected. Iodine value and Lenoleic and Lenolenic acids were increased gradually when plants exposed to water stress at 55% and 70% ASMD meanwhile, saturated fatty acids and Oleic acid decreased with increasing the available soil moisture depletion. Acid value and Refractive index in the analysis of crude sunflower oil were not governed by irrigation regimes in both seasons.   2-Miak cultivar surpassed significantly Elya, Euroflor and Pioneer-6480 cultivars in the vegetative growth and LAI at all sampling dates, and SLA at 60 and 75 days after sowing in both seasons whereas, Elya cultivar exceeded significantly the other three ones in SLA at 45 and 60 days after sowing. Moreover, Elya and Maik cultivars surpassed significantly Euroflor and Pioneer-6480 cultivars in RGR at the period of 60-75, and NAR and CGR at the period of 45-60 days after sowing in both seasons. Miak surpassed significantly the other tested cultivars in seed yield/plot and its components and seed oil percentage in both seasons. Miak and Elya cultivars exceeded significantly Euroflor and Pioneer-6480 in Iodine value whereas, Pioneer-6480 expressed the highest mean values of saturated fatty acids and oleic acid than the other three ones. Miak cultivar surpassed significantly the other tested cultivars in Lenoleic and Lenolenic acids. All tested cultivars did not differ significantly with regard to acid value and refractive index in the analysis of crude sunflower oil in both seasons.  3-Partitioning irrigation sum of squares by means of orthogonal polynomials revealed that linear components caused the majority of varietal response to irrigation regimes in seed yield/plot. Also, the linear slope was positive for all the studied cultivars, indicating that using 40% ASMD increased mean values of seed yield/plot. Appreciable quadratic effect of negative sign was detected in all cultivars except Elya cultivar. Cubic effect, meanwhile, was of negligible in all cases. Therefore, it could be safely concluded that irrigation sunflower cultivars at  40% ASMD would be fruitful in all cultivars except Elya cultivar where water stress may be tolerated.   4-Studies on the relative depression in mean values of number of seeds/head, 1000-seed weight and seed yield/plot resulted from water stress revealed that Elya and Miak cultivars were more tolerant to drought conditions than both of Euroflor and Pioneer-6480 cultivars.   5-Correlation studies revealed that seed yield/plot in sunflower was significantly and positively associated with number of seeds/head, 1000-seed weight when sunflower cultivars received the normal irrigation regime (40% ASMD). At the higher levels of available soil moisture depletion (70% ASMD), however, insignificant association and negatively was detected between seed yield/plot and each of number of seeds/head and seeds weight/head. On the other hand, 1000-seed weight appeared to be significantly and positively correlated with seed yield/plot at all the studied irrigation regimes.