Background : As a part of ongoing research to elucidate and characterize anti-inflammatory nutraceuticals, six kinds of plant extracts (aerial part of Nepeta cataria, leaves of Lonicera maackii, leaves of Platycarya strobilacea, flower of Fagopyrum dibotrys, flowers and fruits of Solanum nigrum, stem of Physostegia virginiana) were tested for their ability to suppress inflammation. The anti-inflammatory has been studied in lipopolysaccharide (LPS)-stimulated RAW264.7 cells which cells synthesized nitric oxide (NO) from L-arginine by nitric oxide synthase (NOS). In this study, NO synthesis inhibitory activity of six kinds of plant extracts on LPS-stimulated RAW 264.7 mouse macrophages was evaluated. Methods and Results : Six kinds of plant extracts were parceled out from RDA (Rural Development Administration). RAW 264.7 cells (1.5×105 cells/well) were seeded onto 96-well plates with DMEM media containing 10% FBS and 1% antibiotics. The cells were pretreated with the extracts and LPS-stimulated cells for 24 h. Cellular NO production was stimulated by adding 1 μg/mL of LPS. After incubation, Griess reagent was used to determine NO production. Absorbance was measured at 520 nm by microplate reader. NO synthesis inhibitory activity potential of these extracts was evaluated by assessing NO production by LPS-stimulated RAW 264.7 cells in the presence. As a result, inhibition rate of NO production was about 40% of L. maackii, 33% of F. dibotrys, 23% of P. strobilacea and 17% of P. virginiana. Meanwhile, there was no significant results in aerial part of N. cataria and flowers and fruits of S. nigrum. Conclusion : From the above results, we be able to confirm that leaves of L. maackii and flower of F. dibotrys appeared dose-dependent NO synthesis inhibitory activity and leaves of P. strobilacea appeared NO synthesis inhibitory activity in low-concentration. As screening NO synthesis inhibition of six extracts, they may be a good candidate for delaying the progression of human inflammatory diseases and warrants further studies.