Two novel β-diketones, 2,6,9-trimethyl-8-decene-3,5-dione (A) and 3,7,10-trimethyl-9-undecene-4,6-dione (B), were identified from the renowned medicinal plant Hypericum perforatum L. The structures of β-diketones A and B were corroborated by syntheses (4 steps starting from methyl acetoacetate,