Oats (Avena sativa) are one of all-value cereals with high quality protein and fat, and also a rich source of β-glucan and bioactive phytochemicals. Thus, oats have attracted research and commercial attention due to those nutritional and functional compounds. The aim of this study was to investigate the functional compounds and antioxidant activity of domestic oat (Avena sativa) cultivars. Oats included three cultivars and two breeding lines: oat cvs. Choyang(CY), Daeyang(DY), Seonyang(SY), Oat61, and Oat62. Chemical compositions were significantly (p<0.05) differed among the oat cultivars, ranging 1.58~1.89% for ash, 11.13~14.37% for crude protein, and 7.89~10.01% for crude fat.  Starch and amylose contents ranged from 56.37 to 64.86 and 15.88 to 18.9%, respectively.  β-glucan, one of functional components known to have the effects of cholesterol lowering, blood glucose regulation, and antitumor activity, ranged from 3.44 to 4.76% in which DY and SY showed higher values of 4.76% and 4.35%, respectively.  Fatty acids compositions were mostly unsaturated fatty acids with oleic acid(43~48%) and linoleic acid(33~40%).  Major amino acids in oat groats were arginine, threonine, tryptophan, valine, and phenylalanine. Total polyphenol contents in oats ranged between 1.67 and 2.49 (mg/g) with the highest in DY and the lowest in Oat61. The 1,1-diphenyl-2-picrylhydrazyl(DPPH) radical scavenging activity was higher in CY and DY (25%), but lower in SY and Oat62 (21%).  A significant correlation (p<0.05) was found free radical scavenging activities and polyphenolic compounds.  This result suggests that the variation in functional components and antioxidant activity could effectively contribute to develop new oat cultivar and to select desired quality traits in oat breeding lines.