1'S-1'-Acetoxychavicol acetate from the rhizomes of Alpinia galanga inhibited nitric oxide (NO) production in lipopolysaccharide-activated mouse peritoneal macrophages with an IC(50) value of 2.3 microM. To clarify the structure-activity relationship of 1'S-1'-acetoxychavicol acetate, various natural and synthetic phenylpropanoids and synthetic phenylbutanoids were examined, and the following structural requirements were clarified. (1) The para or ortho substitution of the acetoxyl and 1-acetoxypropenyl groups at the benzene ring was essential. (2) The S configuration of the 1'-acetoxyl group was preferable. (3) The presence of the 3-methoxyl group and disappearance of the 2'-3' double bond by hydrogenation reduced the activity. (4) The substitution of acetyl groups with propionyl or methyl groups reduced the activity. (5) Lengthening of the carbon chain between the 1'- and 2'-positions reduced the activity.