A new jacaranone derivative, 2-(1,6-dihydroxy-4-oxocyclohex-2-enyl) acetic acid (1), has been isolated from the whole plants of Senecio scandens var. incisus, together with three known compounds: 2'-(p-hydroxyl-cinnamoyl)-6'-jacaranone-D-glucopyranoside (2), 2'-caffeoyl-6'-jacaranone-D-glucopyranoside (3) and kampferol-3-rhamnoside (4). Their structures were elucidated on the basis of spectroscopic data analyses and by comparison with the related known compounds. Cytotoxic activities of 1 against three human tumour cell lines have been evaluated by the MTT method.