Germination does not guarantee plant establishment if there is no efficient and enough reserve mobilization from seeds to the initial seedling growth, mainly in adverse situations. Therefore, this study aimed to evaluate the mobilization of reserves in soybean seeds under water restriction. Four soybean seed lots previously stored for one year were used in the study. To simulate water stress, we used polyethylene glycol (PEG) solutions at concentrations of 0.0, -0.1, and -0.2 MPa. The number of normal, infected and abnormal seedlings were evaluated, along with the number of dead and hard seeds. The radicle, hypocotyl, and cotyledons were separated to determine the dry weight based on the total seed reserve available for mobilization. From this value, the seed reserve reduction, relative dry matter yield, seed reserve reduction rate, and reserve conversion efficiency into dry seedling weight were determined. The increase in water restriction elevates the reserve consumption during the germination process. Vigorous seeds are more efficient in mobilizing and converting grains reserve in dry seedling mass. In less vigorous seeds, mainly those on water restriction, the increase in reserve consumption does not result in conversion into dry seedling mass.