Harmine is a major constituent in a hallucinogenic botanical mixture ayahuasca and medical plant Peganum harmala L. The plant is used for various illnesses and exhibits anti-inflammatory activity. However, the active constituents remain unclear. Here, we screened the seven alkaloids in P. harmala for their anti-inflammatory activity using an nuclear factor-kB (NF-kB) reporter assay. We found that harmine and harmol could inhibit NF-kB transactivity. As the most abundant compound, harmine inhibited tumor necrosis factor-a (TNF-a)- and lipopolysaccharides (LPS)-induced NF-kB transactivity and nuclear translocation in mouse macrophage RAW 264.7 cells. The mRNA and protein levels of NF-kB downstream inflammatory cytokines also reduced. In an LPS-challenged mouse model, harmine markedly averted inflammatory damage of the lung, and decreased serum TNF-a, interleukin-1b (IL-1b) and IL-6 levels. Our data indicate that harmine may exert the anti-inflammatory effect by inhibition of the NF-kB signaling pathway and harmine is probably responsible for the anti-inflammatory effects of P. harmala.