A methanolic extract of the roots of Polygala tenuifolia (Polygalaceae) significantly attenuated nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated BV2 microglia cells. Five xanthones, 1-hydroxy-7-methoxyxanthone (1), 3,6-dihydroxy-1,2,7-trimethoxyxanthone (2), 1,3,6-trihydroxy-2,7-dimethoxyxanthone (3), 1,7-dihydroxy-2,3-dimethoxyxanthone (4) and 1,7-dihydroxy-3-methoxyxanthone (5), and five phenylpropanoids, 4-hydroxy-3-methoxypropiophenone (6), methyl 4-hydroxy-3-methoxycinnamic acid (7), 3,4,5-trimethoxycinnamic acid (8), 4-methoxycinnamic acid (9) and β-d-(3-O-sinapoyl) fructofuranosyl-α-d-(6-O-sinapoyl)glucopyranoside (10), were isolated from CHCl(3) fraction using bioactivity-guided fractionation. Among these compounds, compounds 1, 2, 4, 5 and 7 showed significant inhibitory effects on LPS-induced NO production in BV2 microglia cells at the concentration ranging from 10.0 to 100.0 μM.