<jats:title>Abstract</jats:title><jats:p><jats:boxed-text content-type="graphic" position="anchor"><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image/gif" position="anchor" specific-use="enlarged-web-image" xlink:href="graphic/mcontent.gif"><jats:alt-text>magnified image</jats:alt-text></jats:graphic></jats:boxed-text><jats:p>In addition to the known metabolites cytochalasin H (<jats:bold>1</jats:bold>), cytochalasin J (<jats:bold>2</jats:bold>), and epoxycytochalasin H (<jats:bold>3</jats:bold>), two new 10‐phenyl‐(11)‐cytochalasans, named cytochalasin Z10 and Z11 (<jats:bold>4</jats:bold> and <jats:bold>5</jats:bold>, resp.) were isolated from the solid substrate culture of <jats:italic>Endothia gyrosa</jats:italic> IFB‐E023, an endophytic fungus residing inside the healthy leaf of <jats:italic>Vatica mangachapo</jats:italic> (Dipterocarpaceae). The structure determination of <jats:bold>4</jats:bold> and <jats:bold>5</jats:bold> was accomplished through correlative analyses of their spectral data (UV, ESI‐MS, IR, <jats:sup>1</jats:sup>H‐ and <jats:sup>13</jats:sup>C‐NMR, COSY, NOESY, HMQC, and HMBC). Metabolites <jats:bold>1</jats:bold>–<jats:bold>5</jats:bold> were demonstrated to be substantially cytotoxic to the human leukaemia K562 cell line with the <jats:italic>IC</jats:italic><jats:sub>50</jats:sub> values of 10.1, 1.5, 24.5, 28.3, and 24.4 μ<jats:sc>M</jats:sc>, respectively, which are comparable to that of 5‐fluorouracil (33.0 μ<jats:sc>M</jats:sc>), co‐assayed as the positive reference.