The purpose of this study was to demonstrate the quality characteristics of Brassica juncea cultivated in Jeongseon (BJJ), South Korea. We analyzed the nutritional components and antioxidant activity of BJJ. As a result of the free sugar analysis, the contents of glucose and fructose in BJJ were 0.29±0.02 g/100 g and 0.10±0.00 g/100 g, respectively. The major fatty acids were palmitic acid, octadecenoic acid and stearic acid. The palmitic acid was the highest at 31.22% of all fatty acids. The major minerals were identified as Ca, P, K, Mg and Na. The contents of vitamin B1, vitamin B2, vitamin B6, vitamin C and vitamin E in BJJ were 0.02±0.00 mg/100 g, 0.087±0.01 mg/100 g, 0.02±0.00 mg/100 g, 0.56±0.06 mg/100 g and 0.20±0.03 mg α-TE/100 g, respectively. As a result of the free amino acid analysis, total amino acid contents in BJJ were 2,801.21±115.38 mg/100 g. L-proline content was the highest (744.30±119.06 mg/100 g) in BJJ. BJJ extract inhibits reactive oxygen species production in 3T3-L1 adipocytes. Also, BJJ extract exhibits a protective effect on oxidative stress in H2O2-induced human dermal fibroblast. These results indicate that BJJ comprises various valuable nutrients which can be used as functional food ingredients.