The 80% aqueous acetone extract from the rhizomes of Alpinia galanga showed nitric oxide (NO) production inhibitory activities in mouse peritoneal macrophages. From the aqueous acetone extract, three new 8–9′ linked neolignans, galanganal, galanganols A and B, and a sesquineolignan, galanganol C, were isolated together with nine known phenylpropanoids and p-hydroxybenzaldehyde. The structures of new neolignans were determined on the basis of physicochemical and chemical evidence. In addition, the inhibitory effects of the constituents from the rhizomes of A. galanga on NO production induced by lipopolysaccharide in mouse peritoneal macrophages were examined. Among them, galanganal (IC₅₀=68 μM), galanganols B (88 μM) and C (33 μM), 1′S-1′-acetoxychavicol acetate (2.3 μM), 1′S-1′-acetoxyeugenol acetate (11 μM), trans-p-hydroxycinnamaldehyde (ca. 20 μM), trans-p-coumaryl alcohol (72 μM), and trans-p-coumaryl diacetate (19 μM) were found to show inhibitory activity.