Piper longum L.(Piperaceae), Clerodendrum indicum (L.) Kuntze (Lamiaceae), Acorus calamus L.(Acoraceae) are traditionally used for the treatment of rheumatism, arthritis and other inflammatory conditions in the traditional medicine of India. The present study aimed to investigate the anti-arthritic effect of a polyherbal formulation (PHF) and its underlying mechanism in adjuvant induced arthritis (AIA). Arthritis was induced by intradermal injection of complete Freund’s adjuvant (0.1 ml) into the left hind paw of the Wistar albino rats. PHF (100 & 200 mg/kg b. wt) and prednisolone (PDL)(5 mg/kg b. wt) were administered orally from 1st day to 28th day after adjuvant induction. Induction of arthritis significantly increased hind paw volume (HPV), levels of reactive oxygen species (LPO and NO), and inflammatory cytokines (TNF-α, IL-1β and IL-6) with subsequent decrease in the anti-oxidant status (GSH, SOD and CAT) in arthritic rats compared to controls. Furthermore, the mRNA expression of inflammatory enzymes (iNOS and COX-2), and transcription factor (NF-κB) was found upregulated in the joint tissues of arthritic rats in RT-PCR analysis. On the other hand, the above said imbalances were reverted back effectively to near normal following supplementation with PHF which was supported by the histopathological examination with decreased infiltration of inflammatory cells and synovial hyperplasia eventually protecting further damage of the affected joints. In conclusion, these findings showed that PHF exerted beneficial effects on rheumatoid arthritis in rats.