Soil water status and its effect on plant water status are commonly evaluated for water stress diagnosis in annual crops. We investigated the application of this method to vineyards, using the fraction of transpirable soil water (FTSW) to characterise the soil water deficit experienced by the plant. The stability of the relationship between FTSW and predawn leaf water potential (Ψp) was analysed over two years (2000–2001), in two contrasted soils in vineyards in south eastern France, both planted with the cultivar Syrah, but grafted on different rootstocks (SO4 and 140Ru). FTSW was determined from soil moisture measurements performed with a neutron probe down to 2.5 m, under the rows and between the rows (3 replicates in each case). Vertical and horizontal variations in soil water content were analysed and the upper and lower limits of total vine’s transpirable soil water (TTSW) were calculated for each soil. The lower limit was also compared with the value of soil moisture content determined at −1.5 MPa in the laboratory. FTSW could be calculated for the soil depth analysed, without distinguishing horizontal position (row or inter-row). The lower limit of TTSW for vine was higher than the soil water content at −1.5 MPa, except in the upper horizons (0–0.2 m) which are prone to soil evaporation. A single relationship between Ψp and FTSW was obtained for the two vineyards and for the two years of measurement. This relationship was similar to that established by Lebon et al. (2003) on Gewurztraminer/SO4 in a vineyard in northern France. FTSW can therefore be used as an indicator of the water deficit experienced in vineyards, provided that TTSW is correctly estimated.