Seed development and vigor may be influenced by environmental stresses such as water deficit. Thus, this research was carried out to evaluate the effects of different irrigation treatments and harvest times on seed vigor of four spring safflower cultivars. Treatments were irrigations (irrigations after 70, 100, 130 and 160 mm evaporation, respectively) in main plots and safflower cultivars (Faraman, Goldasht, Sina and Soffeh) in sub-plots. Seeds were harvested in 5 days intervals at 7 stages during development and maturity. The highest and the lowest seed and seedling masss at all harvests and irrigation treatments were recorded for Faraman and Sina cultivars, respectively. Seed vigor of safflower cultivars as measured by electrical conductivity of seed leachates and seedling dry mass decreased with decreasing water availability. Maximum seed mass and seedling dry mass and minimum electrical conductivity were obtained at 40-45 days after flowering, depending on irrigation interval and cultivar. Seed moisture content at these stages was 15-20 %, which is suitable for direct and mechanical harvesting and threshing.