<jats:title>Abstract</jats:title><jats:p>Eight rare pyrrole‐based cytochalasans, termed armochaetoglobins K–R (<jats:bold>1</jats:bold>–<jats:bold>8</jats:bold>), along with three known analogues (<jats:bold>9</jats:bold>–<jats:bold>11</jats:bold>), were isolated from the solid culture broth of <jats:italic>Chaetomium globosum</jats:italic> TW1‐1, a symbiotic fungus derived from the medicinal terrestrial arthropod <jats:italic>Armadillidium vulgare</jats:italic>. Their structures were elucidated using a combination of spectroscopic analysis, a single‐crystal X‐ray diffraction experiment, and an electronic circular dichroism (ECD) calculation. Compounds <jats:bold>4</jats:bold>–<jats:bold>8</jats:bold> represent the first examples of chaetoglobosin‐type cytochalasans with an sp<jats:sup>3</jats:sup> methine carbon at C‐18. All of the isolates were evaluated for their anti‐HIV activities in vitro, and compounds <jats:bold>2</jats:bold>–<jats:bold>4</jats:bold>, <jats:bold>7</jats:bold>, <jats:bold>8</jats:bold>, and <jats:bold>10</jats:bold> showed significant anti‐HIV activities, with EC<jats:sub>50</jats:sub> values ranging from 0.11 to 0.55 μ<jats:sc>M</jats:sc>, and selectivity index (SI) values ranging from 12.33 to 75.42. A plausible biosynthetic pathway was proposed to explain the origin of the pyrrole ring.