A factorial experiment with two factors was carried out at the Seed Technology Lab., College of Agriculture, University of Baghdad in 2018 in order to study the effect of seed priming with gibberellic acid (GA3) (0, 100, 300 and 500 mgL-1) on germination and seedling growth of deteriorated seed of two oat cultivars (Shifaa, and Shofan11). The complete randomized design was used with four replications. The results showed that cultivars, soaking in different concentrations of GA3 and their interactions had a significant effect on studied traits. Shofan11, GA3 (500 mg L-1) and their interaction gave the highest values of germination ratio (74.1, 85 and 85%), lengths of radical (7, 8.5 and 8.6 cm) and plumule (9.3, 10.8 and 10.9 cm), fresh (71.95, 74.74 and 74.76 mg) and dry (18.41, 23.14 and 25.07 mg) weights of seedling and seedling vigour index (1270.2, 1644 and 1655.5), respectively. It can be concluded that soaking of deteriorated seed with GA3 led to increasing germination ratio and improved seedling growth in oat.