In this study, we established the optimal conditions for obtaining water-soluble extracts with antioxidant activity from Kalopanacis cortex. The extraction conditions tested included cold treatment, extraction time (1, 5, 10, 15, and 24 h), and extraction temperature (55, 75, and $95^{circ}C$). The highest total polyphenol compound content from water soluble extracts ($612{mu}g/mL$) was obtained at $95^{circ}C$ for 15 h after cold treatment. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenger activity was also highest (78.8%) under these conditions, which was comparable to 70.2% of ascorbic acid. The hydroxyl radical scavenging activity (HRSA) was also highest (69.0%) under these conditions, stronger than 56.6% of ascorbic acid. These results may provide critical evidence supporting the use of Kalopanacis cortex as a source of antioxidants in functional foods.