To find anti-inflammatory agents based on plant constituents, the effects of six synthetic C-C biflavonoids connecting with different positions of C-C bond between flavone monomers (a: 4′-4′, b: 4′-3′, c: 4′-6, d: 3′-6, e: 6-6, f: 4′-3) were examined on PGE2 and nitric oxide (NO) production from lipopolysaccharide (LPS)-treated macrophages, RAW 264.7. Among the compounds tested, the biflavonoids d, e, and f showed a considerable inhibition of cyclooxygenase-2 (COX-2)-mediated PGE2 production at concentrations up to 50 μM, while the derivative c exerted cytotoxic effects on RAW cells. Especially, the biflavonoid e possessed the most potent inhibitory activity of PGE2 production with an IC50 of 3.7 μM, compared with an IC50 of 8.2–20.7 μM by ginkgetin (natural biflavonoid). Western blot and reverse transcriptase-polymerase chain reaction analyses have shown that the inhibition of PGE2 production by these synthetic derivatives was mediated at least in part by COX-2 inhibition, but not by COX-2 down-regulation. Meanwhile, these synthetic biflavonoids did not considerably inhibit inducible nitric oxide synthase-mediated NO production at concentrations up to 50 μM. When intraperitoneally administered, the biflavonoid e showed a significant anti-inflammatory activity (22.2% inhibition) against rat carrageenan-induced paw oedema at 5 mg kg−1. The biflavonoid e may be used as a synthetic lead for developing new anti-inflammatory agents.