Oleaceae Forsythiae Fructus has been used for anti-inflammatory, diuretics, antidote, and antibacterials in traditional herbal medicine. Our previous screening of medicinal plants showed that methanol (MeOH) extract of Forsythiae Fructus had significant anti-inflammatory activity, but the active ingredients remain unclear. For isolation of active ingredient of MeOH extract of Forsythiae Fructus, it was partitioned with n-hexane and ethylacetate (EtOAc), and arctigenin was isolated from EtOAc fraction by column chromatography with anti-inflammatory activity-guided separation. Its activity was evaluated in the animal models of inflammation including myeloperoxidase (MPO) and eosinophil peroxidase (EPO) activities in the edematous tissues homogenate, and silica-induced reactive oxygen species (ROS) production in the RAW 264.7 cell line. It was shown that arctigenin (100 mg/kg) had significantly decreased not only carrageenan-induced paw edema 3 and 4 h after injection of carrageenan, arachidonic acid (AA)-induced ear edema at a painting dose of 0.1–1.0 mg/ear, and acetic acid-induced writhing response and acetic acid-induced capillary permeability accentuation at an oral dose of 25–100, and 100 mg/kg, respectively, but also MPO and EPO activities at a painting dose of 0.1–1.0 mg/ear in the AA-induced edematous tissues homogenate as indicators of neutrophils and eosinophils recruitment into the inflamed tissue. Further, arctigenin (0.1–10 μM) also significantly inhibited the intracellular ROS production by silica. These results indicate that arctigenin is a bioactive agent of Forsythiae Fructus having significant anti-inflammatory action by inhibition of the exudation, and leukocytes recruitment into the inflamed tissues. The pharmacologic mechanism of action of arctigenin may be due to the inhibition of release/production of inflammatory mediators such as AA metabolites and free radicals.