Background: This present study was conducted to evaluate the anti-inflammatory and immune regulatory effects of Aucklandia lappa Decne (AL). Methods and Results: We measured cytotoxicity, nitric oxide (NO) content, mRNA expression (iNOS, IL-1α, IL-1β, and TNF-α), protein expression (iNOS, COX-2, and IκB-α) and phagocytic activity in RAW264.7 cells. Male BALB/c mice were fed 100 ㎎/㎏ AL (Aucklandia lappa Decneon 70% ethanol extract) and 250 ㎎/㎏ AL for 4 weeks; thereafter, we observed B/T or CD4+/CD8+ lymphocyte subpopulation change, and expression patterns of CD4+ and CD8+ lymphocytes by immunohistochemical staining in mouse splenocytes and/or thymocytes. To determine the experimental concentration of AL, cell viability was measured by MTT assay and tested at 12.5 ㎍/㎖ or less. AL inhibited the levels of NO, lymphokine production (IL-1β, and TNF-α), and mRNA (iNOS, IL-1α, IL-1β, and TNF-α) and protein (iNOS, and COX-2) expression. Additionally, the levels of IκB-α, phagocytic activity, and splenic and thymic T lymphocytes, especially TH and TC cells were significantly increased in AL administered mice. The immuno-reactive density of CD4+ and CD8+ lymphocytes was stronger in AL groups than in the normal group. AL stimulated NO, iNOS, and COX-2, and regulated IL-1α, IL-1β, TNF-α, and IκB-α in macrophages treated with LPS (lipopolysaccharide). In addition, AL increased the phagocytic activity of macrophages and the immunity of mouse T (TH, and TC) cells. Conclusions: These results suggested that AL might show anti-inflammatory activity via the suppression of various inflammatory markers and immuno-regulatory activity.