Curcumin, a component of turmeric (Curcuma longa), is known to exert a variety of biological functions including anti-inflammatory activity. We examined the inhibitory effects of chemically synthesized derivatives of curcumin against inflammatory responses and compared them with those of curcumin, in order to find derivatives with stronger effects than curcumin. In a cell culture system using the mouse macrophage cell line RAW264.7, monoacetylcurcumin strongly inhibited IkappaB phosphorylation, nuclear factor (NF)-kappaB activation and tumor necrosis factor (TNF)-alpha production induced by lipopolysaccharide (LPS). In addition, oral administration of monoacetylcurcumin to mice led to greater suppression of TNF-alpha production after LPS stimulation than the administration of curcumin or tetrahydrocurcumin in vivo. Monoacetylcurcumin also inhibited the LPS-induced NF-kappaB activation in the liver. Collectively, monoacetylcurcumin is a potential chemopreventive agent for treating inflammatory responses more effectively than curcumin.