Puerarin (4'-7-dihydroxy-8-beta-D-glucosylisoflavone), the most abundant isoflavone-C-glucoside extracted from the root of the plant Pueraria lobata, has demonstrated anti-inflammatory activity in cellular models of inflammation. In this report, we examined the ability of puerarin to modulate C-reactive protein (CRP) expression and key molecules in the nuclear factor kappa B (NF-kappaB) pathway to determine its molecular target. The protein and mRNA levels of CRP were determined in lipopolysaccharide (LPS)-induced peripheral blood mononuclear cells of patients with unstable angina pectoris. Also, we detected the I-kappaBalpha phosphorylation and the p65NF-kappaB expression in peripheral blood mononuclear cells under our experimental condition. The results indicated that puerarin inhibited the expression of the protein and mRNA levels of CRP in LPS-induced peripheral blood mononuclear cells. Subsequently, we determined that the inhibition of CRP expression was because of a dose-dependent inhibition of phosphorylation and degradation of inhibitor kappaB(I-kappaB), which resulted in a reduction of p65NF-kappaB nuclear translocation. We conclude that puerarin acts as an anti-inflammatory agent by blocking NF-kappaB signalling, and may possibly be developed as a useful agent for the chemoprevention of atherosclerosis.