In activated macrophage, large amounts of nitric oxide (NO) are generated by inducible nitric oxide synthase (iNOS), resulting in acute or chronic inflammatory disorders. In Raw 264.7 cells stimulated with lipopolysaccharide (LPS) to mimic inflammation, water extracts from the fruit of Chaenomeles sinensis, the root of Polygonum cuspidatum and Boswellia carterii inhibited the LPS-induced NO production in a parallel dose-dependent manner. To investigate the mechanism by which those extracts inhibits NO production, we examined the expression of iNOS and COX-2 in both mRNA and protein levels. We observed a significant change in the iNOS expression between LPS alone and LPS plus those extracts-treated cells. However, water extracts from Chaenomeles sinensis, Polygonum cuspidatum and Boswellia carterii did not inhibit COX-2 expression which was induced by LPS treatment in Raw 264.7 cells. These data suggest that water extracts from Chaenomeles sinensis, Polygonum cuspidatum and Boswellia carterii can modulate anti-inflammatory immune response, which may be in part associated with the regulation of NO synthesis through the regulation of iNOS expression in mouse macrophage cells.