A new cytochalasin dimer, verruculoid A (<b>1</b>), three new cytochalasin derivatives, including 12-nor-cytochalasin F (<b>2</b>), 22-methoxycytochalasin B<sub>6</sub> (<b>3</b>), and 19-hydroxycytochalasin B (<b>4</b>), and 20-deoxycytochalasin B (<b>5</b>), a synthetic product obtained as a natural product for the first time, together with four known analogues (<b>6</b>-<b>9</b>), were isolated and identified from the culture extract of <i>Curvularia verruculosa</i> CS-129, an endozoic fungus obtained from the inner fresh tissue of the deep-sea squat lobster <i>Shinkaia crosnieri</i>, which was collected from the cold seep area of the South China Sea. Structurally, verruculoid A (<b>1</b>) represents the first cytochalasin homodimer containing a thioether bridge, while 12-nor-cytochalasin F (<b>2</b>) is the first 12-nor-cytochalasin derivative. Their structures were elucidated by detailed interpretation of the NMR spectroscopic and mass spectrometric data. X-ray crystallographic analysis and ECD calculations confirmed their structures and absolute configurations. Compound <b>1</b> displayed activity against the human pathogenic bacterium <i>Escherichia coli</i> (MIC = 2 μg/mL), while compounds <b>4</b>, <b>8</b>, and <b>9</b> showed cytotoxicity against three tumor cell lines (HCT-116, HepG-2, and MCF-7) with IC<sub>50</sub> values from 5.2 to 12 μM. The structure-activity relationship was briefly discussed.