A novel 7-O-7′ type mesomeric neolignan, meso-asarolignan A (1), six pairs of new neolignan enantiomers, (±)-asarolignan B–G (2a/2b, 3a/3b, 4–6, 7a/7b), along with 16 known analogues (8–23) were isolated from the rhizomes of Acorus tatarinowii. The structures of the new compounds were elucidated by extensive analysis of spectroscopic, X-ray diffraction, and computational data. Compounds 1–3 represent rare examples of naturally occurring lignans with a 7-O-7′ linkage pattern. All isolated compounds were assayed for their anti-neuroinflammatory effects on tumor necrosis factor α (TNF-α) production in an activated murine microglia cell line. Compounds 7(a/b), 14(a/b), 16, 20, and 22 reduced TNF-α levels without high cell toxicity in LPS-activated BV-2 cells.