Brusatol is a main bioactive component derived from the Chinese medicinal plant Brucea javanica, which is traditionally used for the treatment of dysentery (also known as ulcerative colitis, UC). Previously, we have designed a novel brusatol self-microemulsifying drug delivery system (BR-SMEDDS) to increase its solubility and bioavailability, and enhance its bioactivities. In the present study, we established 2, 4, 6-trinitrobenzenesulfonic acid (TNBS)-induced colitis rat model in vivo and lipopolysaccharide (LPS)-induced RAW 264.7 macrophages in vitro, to investigate the potential anti-inflammatory effect and underlying mechanism of BR-SMEDDS. Disease activity index (DAI) including body weight, stool consistency and gross bleeding was measured. Macroscopic and histological evaluations of colons were conducted. Relevant molecular events were determined by ELISA, qRT-PCR, immunohistochemistry or Western blotting. The results showed that BR notably inhibited the productions of TNF-α, pro-IL-1β, PGE2 and NO, and suppressed the NF-κB signaling pathway in LPS-stimulated macrophages. In parallel with the vitro experimental results, BR significantly attenuated diarrhea, colonic shortening, macroscopic damage and histological injury. BR treatment also increased the levels of TGF-β and IL-4, decreased the contents of IL-1β and IL-18, and elevated the levels of CAT, GSH and SOD in the colons. Furthermore, BR also markedly activated the Nrf2 expression and suppressed the NLRP3 inflammasome activation. Taken together, the anti-UC effect of BR might be intimately associated with the suppression of NF-κB and NLRP3-mediated inflammatory responses, and regulation of Nrf2-mediated oxidative stress. BR might have the potential to be further developed into a promising therapeutic agent for colitis treatment.