Hypermongones A-J (1-10), rare methylated polycyclic polyprenylated acylphloroglucinol derivatives, together with three known simple acylphloroglucinols (11-13) as their plausible biogenetic precursors, were identified from the flowers of Hypericum monogynum. The structures of 1-10 were elucidated by analysis of their 1D and 2D NMR spectroscopic data; the absolute configuration of their polycyclic skeleton was determined by the electronic circular dichroism exciton chirality method and was subsequently confirmed by an X-ray diffraction study of 1. The evaluation of their inhibitory effects on nitric oxide (NO) production in lipopolysaccharide-induced RAW264.7 cells revealed that compound 7 exhibited significant NO inhibition activity, with an IC50 value of 9.5 μM.