A novel quinonoid terpenoid, (-)-α-tocospirone, a new chromanone, (-)-gynuraone, as well as three new steroids, (22E,24S)-7α-hydroperoxystigmasta-5,22-dien-3β-ol, (22E,24S)-stigmasta-1,4,22-trien-3-one, and (24R)-stigmasta-1,4-dien-3-one, together with 15 known components, were isolated from the rhizome of Formosan Gynura japonica. Structures of the new compounds were determined through spectral analyses and chemical evidence. Several of the isolated compounds, caryophyllene oxide, 6-acetyl-2,2-dimethylchroman-4-one, vanillin, 2,6-dimethoxy-1,4-benzoquinone, and benzoic acid exhibited significant anti-platelet aggregation activity in vitro.