Seven new modified fusicoccane-type diterpenoids (<b>1</b>-<b>7</b>), together with two known congeners (<b>8</b> and <b>9</b>), were obtained from <i>Alternaria brassicicola</i>. Their structures were elucidated from a combination of NMR and HRESIMS data and <sup>13</sup>C NMR calculation as well as DP4+ probability analyses, and the absolute configurations of <b>1</b>-<b>5</b> were determined by ECD calculation and single-crystal X-ray diffraction (Cu Kα). Compounds <b>1</b>-<b>3</b> belong to a rare class of 16-<i>nor</i>-dicyclopenta[<i>a,d</i>]cyclooctane diterpenoids, and compounds <b>2</b> and <b>4</b> represent the first examples of fusicoccane-type diterpenoids featuring two previously undescribed tetracyclic 5/6/6/5 ring systems, while compound <b>5</b> features a previously undescribed tetracyclic 5/8/5/3 ring system. Compound <b>7</b> was moderately anti-inflammatory, and compounds <b>2</b>, <b>3</b>, <b>5</b>, and <b>7</b> were weakly cytotoxic.