The present study was carried out to evaluate the anti-inflammatory effect of Spirulina fusiformis on adjuvant-induced arthritis in mice. Arthritis was induced by intra dermal injection of complete freund's adjuvant (0.1 ml) into the right hind paw of Swiss albino mice. Spirulina fusiformis (800 mg/kg/b.wt) was orally administered for 8 d (from 11th to 18th day) to arthritic animals after adjuvant injection. The anti-inflammatory activity of Spirulina fusiformis was assessed by measuring paw volume, body weight, levels of lysosomal enzymes, tissue marker enzymes and glycoproteins in control and experimental animals. In adjuvant-induced arthritic animals, the levels of lysosomal enzymes, tissue marker enzymes, glycoproteins and the paw volume were increased significantly. However the body weight was found to be reduced when compared to control animals. Oral administration of Spirulina fusiformis (800 mg/kg/b.wt) significantly altered these above physical and biochemical changes observed in arthritic animals to near normal conditions. Hence results of this study clearly indicate that Spirulina fusiformis has promising anti-inflammatory activity against adjuvant-induced arthritic animals. © 2006 Pharmaceutical Society of Japan.