To study the effects of seed size and priming under different light conditions on germination and seedling growth of corn, an experiment was conducted at the Seed Research Laboratory of Razi University, Kermanshah, Iran. The experiment was a factorial with three factors arranged in a completely randomized design with four replications. The first factor was seed size at three levels (large, medium and small), the second was seed priming agent at four levels (control (unprimed), distilled water, KNO3 and HB-101 (a purely natural extract), and the third was priming condition at two levels (in the presence of light and darkness). Results indicated that both priming treatment and seed size had significant effects on the traits under study including seed germination percentage, mean germination... rate, radicle length, plumule length, radicle dry weight, plumule dry weight and seedling vigor index. All priming treatments significantly improved the traits under study compared with the control. However, the seeds primed with KNO3 or HB-101 notably performed better than those primed with distilled water. In all of the evaluated traits, large seeds showed higher values than medium and small seeds. However, in some of the studied traits, there were no significant differences between large and medium seed sizes when corn seeds were primed. The traits under study were not significantly influenced by priming conditions (priming in the presence of light or darkness).