Technical Abstract: Garlic has been used as a folk medicine for a long history. Numerous studies demonstrated that garlic extracts and its sulfur-containing compounds inhibit nuclear factor-kappa B (NF-kB) activation induced by various receptor agonist including lipopolysaccharide (LPS). These effects suggest that garlic extracts have anti-cancer and anti-inflammatory effects. However, the mechanism as to how garlic extracts mediate the health effects is largely unknown. Toll-like receptors (TLRs) play a key role in sensing diverse microbial products and inducing innate immune responses. The LPS-induced dimerization of TLR4 is required for the activation of NF-kB that is the central mediator of the immune responses. Therefore, TLR4 dimerization may be one of the first lines of regulation in activating LPS-induced signaling pathways. Here, we report biochemical evidence that ethyl acetate fraction of garlic inhibits the LPS-induced dimerization of TLR4 resulting in the inhibition of NF-kB activation and expression of cyclooxygenase 2 and inducible nitric oxide synthase. Our results first demonstrate that garlic extracts can directly inhibit TLRs-mediated signaling pathway at the receptor level. These results shed a new insight in understanding how garlic modulates the immune responses that could modify the risk of many diseases.