Seed quality is one of the most important factors affecting seed germination and seedling growth. In order to investigate the effects of seed aging on germination and seedling growth of sunflower cultivars, a factorial experiment was conducted based on a completely randomized design with three replications in seed research laboratory of Shirvan Higher Education Complex. To create 7 different treatments of seed aging, seeds of three cultivars Ghasem, Farrokh and Barzgar (as the first factor) were kept at a high temperature (43◦ C) and high relative humidity (100%) for 0 (control), 24, 48, 72, 96, 120 and 144 hours (as a second factor). The results of mean comparison showed that germination percentage, rate and seedling growth of Farrokh cultivar was more than other cultivars in each aging level. Germination percentage, rate and uniformity, seedling dry weight, radicle and stem length reduced linearly with increase in the duration aging in all cultivars. Under the aging conditions, the time to beginning and ending of germination was significantly increased. Overall, it was concluded that seed quality of sunflower cultivars was seriously decreased under the aging conditions.