An experiment was conducted at Rimski Šančevi Experiment Field of Institute of Field and Vegetable Crops in Novi Sad during 2000- 2005. The soil in the experimental plot was calcareous chernozem on loess terrace. Using the yield response factor (ky), the study investigated how sunflower yield and eva potranspiration were affected by deficit of available soil water during the grow ing season. The experiment consisted of an irrigated treatment (T1), in which irrigation was used when soil moisture levels dropped to 60-65% of FC (field capacity), and a nonirrigated control treatment (T0). The sunflower hybrid used in the study was NS-H-111. On average, no significant differences in yield level were observed between T1 (3.79 t ha-1) and T0 (3.75 t ha-1) treatments. Seasonal evapotranspiration (ETm) obtained in T1 treatment was in the 402-479 mm range. The yield response factor (ky) was obtained as 0.20 for total growing season and 0.27, 0.31 and 0.48 for vegetative, flowering and yield formation period, respectively. Period from flowering to maturity was the most sensitive towards water defi ciency.