Onion (Allium cepa L.) seeds lose viability within 1 -2 years and exhibit a short lifespan. In this study, a factorial experiment in a randomized complete block design with six replications was conducted to determine the effects of soaking seeds for 24 h in distilled water (DW); aerated distilled water (ADW), 0.1% of each (succinic acid, aerated succinic acid (ASA), ascorbic acid, aerated ascorbic acid, nitroben (N), and aerated nitroben (AN) separately; and control (germinating seeds on filter paper with DW), and incubating at a constant temperature of 20°C in the dark. Seeds soaked in ASA showed the highest germination, speed of germination index (SGI), seedling vigor index, seedling dry weight and seedling length (cm). High SGI was also noted in seeds soaked in AN. Seeds soaked in N showed high germination rate and germination energy. The highest values of germination time GT, abnormal seedling percentage, and dead seed percentage were recorded with control treatment. Thus, the germination methods affected the germination traits as well as seedling growth of onion seeds.