Indirubin is the active ingredient of Danggui Longhui Wan, a mixture of plants that is used in traditional Chinese medicine to treat chronic diseases. In this study we investigated the anti-inflammatory effects of an indirubin derivative, indirubin-3'-monoxime-5-sulphonic acid (I3M-5S, C<sub>16</sub>H<sub>11</sub>N<sub>3</sub>O<sub>5</sub>S). We found that I3M-5S inhibits the production of various inflammatory mediators such as nitric oxide (NO) and prostaglandin E<sub>2</sub> (PGE<sub>2</sub>) as well as inflammatory cytokines, tumor necrosis factor-α and interleukin-6 in lipopolysaccharide (LPS) stimulated murine macrophage, RAW264.7 cells. In addition, the expression of inducible nitric oxide synthase and cyclooxygenase-2, which are essential enzymes to produce NO and PGE<sub>2</sub>, respectively, was blocked by I3M-5S treatment in LPS-stimulated RAW264.7 cells. Present data suggest that I3M-5S exhibits potent anti-inflammatory activity in cultured macrophages and merit further study as potential therapeutic agents for inflammatory disorders.