The present study was undertaken to investigate the anti-arthritic activity of a biopolymeric fraction (BET) from plant Euphorbia tirucalli Boiss (Euphorbiaceae). The fraction showed dose dependent anti-arthritic activity and also showed in vivo immunomodulatory capacity being a major component in inhibiting arthritis. It caused suppression of CD4(+) and CD8(+) T cells, inhibition of intracellular Interleukin-2 (IL-2) and Interferon-gamma (IFN-gamma) by flowcytometry. It inhibited vascular permeability and the migration of leucocytes at the site of the insult. The oral LD(0) in both rats and mice was more than 2000 mg/kg.