Winegrowers must adapt more and more their viticultural practices in order to evolve toward a sustainable viticulture, to be competitive and to improve both the production methods and the quality and typicalness of wines. In this context, ‘Terroir’ studies in Loire Valley vineyards have allowed to build decision aid maps that can be used directly by growers to adjust their practices. We focus here on the vigor potential conferred by soil (VIPOS) that especially allows adapting the choice of the rootstock. An algorithm had previously been proposed by Morlat (2001) to estimate VIPOS according to three main influencing variables: water holding capacity of the soil, gravel percentage on the soil profile and parent rock hardness. Nevertheless, the VIPOS estimation, based on this algorithm, had to be completed by expertise. The objective of the paper is to present a new method to estimate VIPOS using a fuzzy expert system that allows having an automatically continuous estimation