OBJECTIVE To explore the anti-inflammatory effect of triptolide (TPT) by regulating miR-155 in monocytes pre-stimulated by lipopolysaccharide (LPS) from rheumatoid arthritis (RA) patients. METHODS Monocytes were isolated by CD14⁺ magnetic beads from peripheral blood mononuclear cells (PBMCs) of RA and stimulated by LPS for 24 hours. The levels of tumor-necrosis factor-α (TNF-α) and interleukin 6 (IL-6) in monocytes were detected by ELISA and the expression of miR-155 was measured by real-time quantitative PCR (qRT-PCR) in monocytes before and after the treatment of TPT at different concentrations. MiR-155 mimic and negative control were respectively transfected into the LPS-stimulated monocytes by Lipofectamine(TM)2000. Twenty-four hours later, the monocytes were treated with or without TPT for another 24 hours. TNF-α and IL-6 expressions in the cell culture supernatants were detected by ELISA and the expressions of suppressor of cytokine signaling-1 (SOCS1) and Src homology 2 domain-containing inositol 5-phosphatase 1 (SHIP-1) were tested by Western blotting. RESULTS TPT suppressed the expressions of TNF-α, IL-6 and miR-155 in LPS-stimulated peripheral blood monocytes from RA patients. Over-expression of miR-155 significantly reversed the down-regulation of TNF-α and IL-6 by TPT in monocytes. TPT up-regulated the expressions of SOCS1 and SHIP-1 in monocytes, but over-expressed miR-155 antagonized the effect of TPT on SHIP-1 while the expression of SOCS1 was not affected. CONCLUSIONS TPT suppressed the expression of miR-155 and up-regulated the release of SHIP-1, thus inhibiting the inflammatory response in the LPS-stimulated monocytes of RA patients.