<jats:title>Abstract</jats:title><jats:p>Bioassay‐guided fractionation of the root wood of <jats:italic>Magnolia kachirachirai</jats:italic> (<jats:sc>Kanehira</jats:sc> & <jats:sc>Yamamoto</jats:sc>) <jats:sc>Dandy</jats:sc> (Magnoliaceae) led to the isolation of three new compounds, kachiraterpenol (<jats:bold>1</jats:bold>), (<jats:italic>E</jats:italic>)‐2,3‐bis(4‐hydroxy‐3‐methoxyphenyl)prop‐2‐enal (<jats:bold>15</jats:bold>), and kachiranol (<jats:bold>19</jats:bold>), together with 27 known compounds, of which 4,4′‐dihydroxy‐3,3′‐dimethoxybenzophenone (<jats:bold>16</jats:bold>) was isolated for the first time from a natural source. Their structures were elucidated by spectroscopic analysis. Two of these isolates, costunolide (<jats:bold>2</jats:bold>) and dehydrosaussurea lactone (<jats:bold>4</jats:bold>), showed cytotoxic properties against MCF‐7, NCI‐H460, and SF‐268 cancer cell lines <jats:italic>in vitro.</jats:italic>