Extraction of water soluble antioxidant materials from garlic husk (GH) was investigated using two hydrothermal methods, steam explosion (SE, 200 and 213 °C for 5 min) and microwave irradiation method (MW, 180 and 200 °C for 2 and 5 min). Water extract was evaluated by EC50 value (a concentration at a radical scavenging activity of 50%) and amount of phenolic compounds (expressed as catechin equivalent). Compared with the EC50 value (12.73 g/l) and amount of phenolic compounds (1.9 mg-catechin equiv./g-dry treated GH) of extract obtained from treated GH by conventional heating method using autoclave (121 °C for 10 min) combined with milling, the EC50 value decreased (increased the radical scavenging activity) and the amount of phenolic compounds increased dramatically with the extract obtained from treated GH by SE and MW, respectively. The lowest EC50 value (0.26 g/l) and the highest amount of phenolic compounds (40.0 mg-catechin equiv./g-dry treated GH) were attained by MW at treatment temperature of 200 °C for 5 min. Furthermore, relationship of EC50 value of extract obtained from treated GH by SE and MW and severity factor of each treatment condition indicated that appropriate severity factor to extract antioxidant material from GH highly using two hydrothermal methods, i.e. SE and MW could be around 3.0.