Galgeuntang water extract exhibited a strong free radical scavenging activity and reducing powerdetermination. However, a gradual increase in the free radical scavenging activity and reducingpower determination was obtained with increasing concentrations. The highest radicalscavenging activity was shown by the water extract from Galgeuntang (116.93 μg/mL) and thewater extract from Cinnamonum cassia Presl. (95.01 μg/mL). These results of phenolic andflavonoid contents of the extracts indicated that the strong radical scavenging activity of theCinnamonum cassia Presl. extract might be in part due to the phenolic compounds. The correlationcoefficient between TPC and DPPH (r2 = 0.9312), TFC and DPPH (r2 = 0.9677), showed positivecorrelation among total phenolic/flavonoid contents and antioxidant activity. These resultssuggest that Galgeuntang has a potential antioxidant activity.