Studies on soil moisture conditions for onion crop are important to state of São Paulo, primarily because in the regions where onion is cultivated, supplementar water is necessary. The experiment was conducted by using onion sets propagation, furrow irrigation method, and the standard gravimetric method for soil moisture content determination the treatments were differentiated by the allowed minimal water potential before each irrigation, as follow: -0,5; -1,0; -6,0 and -15,0 bars. The following conclusions were obtained under the climatic conditions observed during the experiment, soil, variety and methods used. a) positive responses to high soil moisture potentials (-0,5 bar) were observed in the data related to bulb weight, bulb and stalk diameter, leaf weight; b) maturity, number of leaves and incidence of Alternaria porri, Ellis, were not significantly by the treatments used.