<p>The chemical investigation of the leaves and stem bark of <i>Acacia polyacantha</i> (Fabaceae) led to the isolation of a new oleanane-type triterpenoid saponin named polyacanthoside A <b>1</b> together with fifteen known compounds. Their structures were established from spectral , mainly HRESIMS, 1D NMR and 2D NMR and by comparison with literature data. The cytotoxicity of compound <b>1</b> and the analogues <b>8</b> as well as doxorubicin was determined in a panel of 9 cancer cell lines including sensitive and drug resistant phenotypes. Unlike the analogue <b>8,</b> compound <b>1</b> as well as doxorubicin displayed cytotoxic effects in all the 9 tested cancer cell lines with IC<sub>50</sub> values ranged from 8.90 μM (towards CCRF-CEM leukemia cells) to 35.21 μM (towards HepG2 hepatocarcinoma cells) for compound <b>1</b> and from 0.02 μM (towards CCRF-CEM leukemia cells) to 66.83 μM (against CEM/ADR5000 leukemia cells) for doxorubicin.</p
