Seaweed and their constituents have been traditionally employed for the management of various human pathologic conditions such as edema, urinary disorders and inflammatory anomalies. The current study was performed to investigate the antioxidant and anti-arthritic effects of fucoidan from Undaria pinnatifida. A noteworthy in vitro antioxidant potential at 500 mu g/ml in 2, 2-diphenyl-1-picrylhydrazyl scavenging assay (80% inhibition), nitrogen oxide inhibition assay (71.83%), hydroxyl scavenging assay (71.92%), iron chelating assay (73.55%) and a substantial ascorbic acid equivalent reducing power (399.35 mu g/mg ascorbic acid equivalent) and total antioxidant capacity (402.29 mu g/mg ME) suggested fucoidan a good antioxidant agent. Down regulation of COX-2 expression in rabbit articular chondrocytes in a dose (0-100 mu g) and time (0-48 h) dependent manner, unveiled its in vitro anti-inflammatory significance. In vivo carrageenan induced inflammatory rat model demonstrated a 68.19% inhibition of inflammation whereas an inflammation inhibition potential of 79.38% was recorded in anti-arthritic complete Freund's adjuvant-induced arthritic rat model. A substantial ameliorating effect on altered hematological and biochemical parameters in arthritic rats was also observed. Therefore, findings of the present study prospects fucoidan as a potential antioxidant that can effectively abrogate oxidative stress, edema and arthritis-mediated inflammation and mechanistic studies are recommended for observed activities. (C) 2017 Elsevier B.V. All rights reserved.