Objective: Sinomenine (SIN), an alkaloid isolated from sinomenium acutum plant, possesses many pharmacological properties, such as anti-inflammation, anti-hyperalgesia, anti-allergy, anti-apoptosis, and anti-angiogenesis. In this study, we aimed to investigate the detailed molecular mechanisms associated with the anti-inflammatory activity of SIN in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Methods: RAW264.7 cells were treated with LPS and/or indicated concentrations of SIN. Inflammatory cytokine production, such as TNF-alpha, IL-1 beta, and IL-6, was detected by ELISA. Expression of microRNA-155 (miR-155), SOCS1 and NF-kappa B was assessed by qRT-PCR and Western blot, separately. Simultaneously, miR-155 inhibitor and SOCS1 SiRNA were transfected to observe the regulative effects of SIN on the expression of miR-155, SOCS1, and NF-kappa B. Results: Our result showed that SIN treatment significantly reduced LPS-induced inflammatory cytokine release, suppressed the expression of miR-155, enhanced SOCS1 expression at mRNA and protein levels, and prevented NF-B transcription. Furthermore, transfection of miR-155 inhibitor and SOCS1 SiRNA emphasized that the regulation of miR-155, SOCS1, and NF-B was associated with the anti-inflammatory activation of SIN in LPS-treated macrophages. Conclusions: This study indicated that SIN alleviated LPS-induced inflammatory responses in RAW264.7 macrophages by downregulating miR-155 and upregulating SOCS1, at least partly, leading to the suppression of NF-B transcription. These findings suggest that SIN might be developed as an alternative and promising drug for the treatment of inflammatory diseases.