In this study, the main purpose is to determine the ultrasound-assisted extraction (UAE) conditions for extracting phenolic compounds obtained from Alpinia galanga (L.) Willd. rhizome. The influences of extraction factors (type of solvent, solvent concentration, solid[1]to-liquid (SL) ratio, time and temperature) on the total polyphenol content (TPC) and 2,2-diphenyl-1-picrylhydrazyl free radical scavenging capacity (DPPHRSC) were investigated. The findings pointed out that all of these factors significantly affected TPC and DPPHRSC. The highest TPC and DPPHRSC obtained from A. galanga root extract were 7.49 ± 0.19 mg GAE g-1 DM and 90.34 % at the acetone concentration of 60 % (v/v), SL ratio of 1:25, extraction time of 20 min and extraction temperature of 40oC. The microstructure of the sample before and after extraction significantly changed under ultrasound radiation.