The phytochemical investigation on the roots of Acanthopanax henryi (Araliaceae) resulted in the discovery of twenty compounds whose chemical structures were elucidated by the analysis of 1D-, 2D-NMR, mass spectrometry data, other physicochemical properties, and a comparison of the spectral data with the literature. They were identified as (-)-sesamin (1), helioxanthin (2), savinin (3), taiwanin C (4), 6-methoxy-7-hydroxycoumarin (5), behenic acid (6), 3-O-caffeoyl-quinic acid (7), 5-O-caffeoyl-quinic acid (8), 1,3-di-O-caffeoyl-quinic acid (9), 1,4-di-O-caffeoyl-quinic acid (10), 1,5-di-O-caffeoyl-quinic acid (11), (+)-threo-(7R,8R)-guaiacylglycerol-β-coniferyl aldehyde ether (12), (+)-erythro-(7S,8R)-guaiacylglycerol-β-coniferyl aldehyde ether (13), ferulic acid (14), caffeic acid (15), stigmasterol (16), β-sitosterol (17), adenosine (18), syringin (19), and trans-coniferin (20). Among these isolates, compound 3 showed inhibitory activity against lipopolysaccharide- (LPS-) induced nitric oxide (NO) and prostaglandin E2 (PGE2) production with IC50 values of 2.22 ± 0.11 and 2.28 ± 0.23 μM, respectively. The effects of compound 3 were associated with the suppression of LPS-induced expression of the inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein. Furthermore, compound 3 negatively regulated the production of interleukin- (IL-) 1β and tumor-necrosis factor- (TNF-) α at the transcriptional level in LPS-stimulated BV2 microglial cells. These antineuroinflammatory effects of compound 3 were mediated by p38 mitogen-activated protein kinase (MAPK).