Rheumatoid arthritis is a chronic inflammatory disorder of autoimmune origin that preferentially attacks smaller synovial joints of legs and hands to later period it will develops and affect body tissues and organs that causing permanent disability. Recently, there is no complete curable treatment for Rheumatoid arthritis but symptoms are suppressed on an individual basis. This study is aimed to evaluate the potential activity of Excoecaria agallochaL. (Euphorbiaceae) against Rheumatoid arthritis. Excoecaria agallochais a mangrove plant. It is widely present in the coastal region mainly in Tamilnadu (Adirampattinam, Chidambaram). It has potential pharmacological activity against several diseases particularly for pain related disease. Ethno medically it has anti-rheumatism,anti-paralysis, anti-epileptic, anti-leprosy and anti-psoriatic activity. In order to perform this study, 70% hydroalcoholic extract was obtained by using Soxhlet extraction method. In-vitro studies were performed for anti-inflammatory and anti-arthritic activity using membrane stabilization and protein denaturation method. Both assays give significant activity against inflammation and arthritis. The inhibitory concentration of membrane stabilization (anti-inflammatory assay) and protein denaturation (anti-arthritic assay) were found to be IC50 220.92 ?g/mlandIC50 436.56 ?g/ml respectively. The in-vivo study was performed for 21 days by using formalin induced rheumatoid arthritis in rats. The percentage inhibition of paw volume was recorded for both 200mg/kg and 400mg/kg of HAEEA and it was found to be 30.12 % and 41.34 % respectively. Hence Excoecaria agallochahas shows good activity against rheumatoid arthritis.