<jats:title>Abstract</jats:title><jats:p>One new pimarane‐type diterpenoid (<jats:bold>1</jats:bold>) and two new taraxerane‐based triterpenoids (<jats:bold>2</jats:bold> and <jats:bold>3</jats:bold>) were isolated from the bark of <jats:italic>Macaranga tanarius</jats:italic>, along with seven known compounds. Their structures were identified by spectroscopic methods including NMR and MS analyses. Compounds <jats:bold>1</jats:bold>–<jats:bold>5</jats:bold> were tested for their <jats:italic>in vitro</jats:italic> inhibition of DNA topoisomerase II, as well as for their cytotoxicities against human lung carcinoma A549 cells (<jats:italic>Table 3</jats:italic>). The triterpenoids <jats:bold>2</jats:bold>–<jats:bold>5</jats:bold> showed strong activities in both assays, but the diterpenoid <jats:bold>1</jats:bold> was only moderately active.