Objective. To investigate the molecular mechanisms of the antiarthritic effects of bee venom (BV) and melittin (a major component of BV) in a murine macrophage cell line (Raw 264.7) and in synoviocytes obtained from patients with rheumatoid arthritis. Methods. We evaluated the antiarthritic effects of BV in a rat model of carrageenan-induced acute edema in the paw and in a rat model of chronic adjuvant-induced arthritis. The inhibitory effects of BV and melittin on inflammatory gene expression were measured by Western blotting, and the generation of prostaglandin E2 (PGE2) and nitric oxide (NO) and the intracellular calcium level were assayed. NF-κB DNA binding and transcriptional activity were determined by gel mobility shift assay or by luciferase assay. Direct binding of BV and melittin to the p50 subunit of NF-κB was determined with a surface plasmon resonance analyzer. Results. BV (0.8 and 1.6 μg/kg) reduced the effects of carrageenan- and adjuvant-induced arthritis. This reducing effect was consistent with the inhibitory effects of BV (0.5, 1, and 5 μg/ml) and melittin (5 and 10 μg/ml) on lipopolysaccharide (LPS; 1 μg/ml)-induced expression of cyclooxygenase 2, cytosolic phospholipase A2, inducible NO synthase, generation of PGE2 and NO, and the intracellular calcium level. BV and melittin prevented LPS-induced transcriptional and DNA binding activity of NF-κB via the inhibition of IκB release and p50 translocation. BV (affinity [Kd] = 4.6 × 10-6M) and melittin (K d = 1.2 × 10-8M) bound directly to p50. Conclusion. Target inactivation of NF-κB by directly binding to the p50 subunit is an important mechanism of the antiarthritic effects of BV.