To study the inhibitory effect of the ethyl acetate extract of Aquilaria crassna0 on lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-) secretion from isolated human peripheral blood mononuclear cells and its mechanisms of anti-inflammation so as to provide some evidence for its traditional use. Human peripheral blood mononuclear cells (hPBMCs) were isolated from healthy volunteers. Cells, at a concentration of 110 6 cell/ml, were induced to secrete TNF-by exposure to 10 ng/ml LPS in the presence and absence of the ethyl acetate extract of Aquilaria crassna. The TNF-a secretion in the collection medium was measured by enzyme-linked immunosorbent assay and the TNF-gene expression was measured by reverse transcriptase-polymerase chain reaction. Determination of ERK1/2 MAPK and p38 MAPK activation were performed by Western blot analysis using a specific phosphorylated form of ERK1/2, p38 MAPK antibody. LPS at a concentration of 10 ng/ml significantly increased in TNF-a secretion and was significantly inhibited when treated with 1.5 mg/ml ethyl acetate extract of Aquilaria crassna (P< 0.05). Moreover, on treatment with 1.5 mg/ml, the extracts showed TNF-gene expression inhibition. Co-treatment of the extract with LPS could not block p38 MAPK activation, but pre-treatment of the extracts significantly reduced the p38 MAPK phosphorylation without affecting the ERK1/2 MAPK activation (P< 0.05). The ethyl acetate extract of Aquilaria crassna inhibits TNF-gene expression and secretion in LPS-induced hPBMCs. This inhibitory effect apparently resulted from selectively attenuating the p38 MAPK activation.