| Summary: | In a series of anti-inflammatory screenings of lauraceous plants, the methanolic extract of the leaves of <i>Machilus japonica</i> var. <i>kusanoi</i> (Hayata) J.C. Liao showed potent inhibition on both superoxide anion generation and elastase release in human neutrophils. Bioassay-guided fractionation of the leaves of <i>M. japonica</i> var. <i>kusanoi</i> led to the isolation of twenty compounds, including six new butanolides, machinolides A–F (<b>1</b>–<b>6</b>), and fourteen known compounds (<b>7</b>–<b>20</b>). Their structures were characterized by 1D and 2D NMR, UV, IR, CD, and MS data. The absolute configuration of the new compounds were unambiguously confirmed by single-crystal X-ray diffraction analyses (<b>1</b>, <b>2</b>, and <b>3</b>) and Mosher’s method (<b>4</b>, <b>5</b>, and <b>6</b>). In addition, lignans, (+)-eudesmin (<b>11</b>), (+)-methylpiperitol (<b>12</b>), (+)-pinoresinol (<b>13</b>), and (+)-galbelgin (<b>16</b>) exhibited inhibitory effects on <i>N</i>-formyl-methionyl-leucyl-phenylalanine/cytochalasin B (fMLP/CB)-induced superoxide anion generation in human neutrophils with IC<sub>50</sub> values of 8.71 ± 0.74 μM, 2.23 ± 0.92 μM, 6.81 ± 1.07 μM, and 7.15 ± 2.26 μM, respectively. The results revealed the anti-inflammatory potentials of Formosan <i>Machilus japonica</i> var. <i>kusanoi.</i>
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