<div><p>We have studied the ethyl acetate fraction of the methanolic extract of the root barks of <i>Calotropis procera</i> (Asclepiadaceae) from Egypt. Bioassay-directed fractionation and final purification of the extract resulted in the identification of a new cardenolide glycoside named proceraside A (<b>1</b>) together with two known compounds, frugoside (<b>2</b>) and calotropin (<b>3</b>). Their structures were elucidated by extensive NMR studies and mass spectrometric data. The <i>in vitro</i> cytotoxicity of the isolated compounds was evaluated against A549 non-small cell lung cancer, U373 glioblastoma and PC-3 prostate cancer cell lines. They showed potent activity against the tested cancer cell lines with IC<sub>50</sub> ranging from 0.005 to 0.3 μg/mL. Cisplatin was used as positive control.</p></div
