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Objective To investigate the molecular mechanisms that are responsible for anti-inflammatory effect of usnic acid (UA), the effects of UA from usnea longissm on tumor necrosis factor-α(TNF-α) and nitric oxide (NO) production in peritoneal macrophages has been examined. Methods The different concentrations of UA were added to peritoneal macrophages. The TNF-α and NO production in peritoneal macrophages were examined with mouse TNF-α ELISA kit and NO content by measuring the amount of nitrite (NO-2μmol/L) formed in the medium using Griess reaction. The activity of inducible nitric oxide synthase (i-NOS) was determined using i-NOS detection kit and the TNF-α mRNA expression was tested by reverse transcriptase polymerase chain reaction (RT-PCR). Results UA decreased the TNF-α and NO level in LPS-stimulated peritoneal macrophages in dose-dependent manner, the IC50 values were 12.8μmol/L and 5.7μmol/L respectively. RT-PCR analysis indicated that UA could inhibit TNF-α mRNA expression; the activity analysis of i-NOS indicated that UA could inhibit the activity of i-NOS. Conclusion UA could inhibit the TNF-α and NO production in peritoneal macrophages, it may be associated with the anti-inflammatory activity of UA.