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The roots of <i>Melastoma malabathricum subsp. normale</i> (D. Don) Karst. Mey have been used in traditional ethnic medicine systems in China to treat inflammation-triggered ailments, such as trauma, toothache, and fever. Therefore, the aim of this study is to screen for compounds with anti-inflammatory activity in the title plant. The extract of <i>M</i>. <i>malabathricum subsp. normale</i> roots was separated using various chromatographic methods, such as silica gel, ODS C18, MCI gel, and Sephadex LH-20 column chromatography, as well as semi-preparative HPLC. One new complex tannin, named whiskey tannin D (<b>1</b>), and an undescribed tetracyclic depsidone derivative, named guanxidone B (<b>2</b>), along with nine known polyphenols (<b>2</b>–<b>10</b>) and three known depsidone derivatives (<b>12</b>–<b>14</b>) were obtained from this plant. The structures of all compounds were elucidated by extensive NMR and CD experiments in conjunction with HR-ESI-MS data. All these compounds were isolated from this plant for the first time. Moreover, compounds <b>1</b>–<b>4</b>, <b>8</b>, and <b>10</b>–<b>14</b> were obtained for the first time from the genus <i>Melastoma</i>, and compounds <b>1</b>, <b>2</b>, and <b>11</b>–<b>14</b> have not been reported from the family Melastomataceae. This is the first report of complex tannin and depsidone derivatives from <i>M. malabathricum subsp. normale</i>, indicating their chemotaxonomic significance to this plant. Compounds <b>1</b>–<b>12</b> were investigated for their anti-inflammatory activities on the production of the nitric oxide (NO) in lipopolysaccharide (LPS)-stimulated RAW264.7 cells, and compounds <b>1</b>, <b>11</b>, and <b>12</b> showed anti-inflammatory activities with IC₅₀ values of 6.46 ± 0.23 µM, 8.02 ± 0.35 µM, and 9.82 ± 0.43 µM, respectively. The structure–activity relationship showed that the catechin at glucose C-1 in ellagitannin was the key to its anti-inflammatory activity, while CH₃O- at C-16 of aromatic ring A in depsidone derivatives had little effect on its anti-inflammatory activity. The study of structure–activity relationships is helpful to quickly discover new anti-inflammatory drugs. The successful isolation and structure identification of these compounds, especially complex tannin <b>1</b>, not only provide materials for the screening of anti-inflammatory compounds, but also provide a basis for the study of chemical taxonomy of the genus <i>Melastoma</i>.