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<i>Clausena lenis</i> Drake (<i>C. lenis</i>) is a folk medicinal herb to treat influenza, colds, bronchitis, and malaria. The 95% and 50% ethanol extract of <i>C. lenis</i> showed significant nitric oxide (NO) inhibition activity in BV-2 microglial cells stimulated by lipopolysaccharide (LPS). Bio-guided isolation of the active extract afforded five new compounds, including a chlorine-containing furoquinoline racemate, (±)-claulenine A (<b>1</b>), an amide alkaloid, claulenine B (<b>2</b>), a prenylated coumarin, claulenin A (<b>3</b>), a furocoumarin glucoside, clauleside A (<b>4</b>), and a multi-prenylated <i>p</i>-hydroxybenzaldehyde, claulenin B (<b>5</b>), along with 33 known ones. Their structures were determined via spectroscopic methods, and the absolute configurations of new compounds were assigned via the electronic circular dichroism (ECD) calculations and single-crystal X-ray diffraction analysis. Compounds <b>2</b>, <b>23</b>, <b>27</b>, <b>28</b>, <b>33</b>, and <b>34</b> showed potent anti-neuroinflammatory effects on LPS-induced NO production in BV-2 microglial cells, with IC₅₀ values in the range of 17.6–40.9 μM. The possible mechanism was deduced to interact with iNOS through molecular docking.