The aim of this study was to assess the effects of water deficit on the development of fava beans, as well as to determine the coefficient of sensitivity to water deficit (Ky) in the phenological phases in a protected environment. The experiment was carried out in pots in a greenhouse, covered with 15 m thick low density polythene, in the experimental area of the Teresina Agricultural College of the Federal University of Piauí (UFPI), Teresina-PI.