Technical Abstract: Toll-like receptors play a key role in sensing microbial components and inducing innate immune responses. Ligand-induced dimerization of Toll-like receptor (TLR) 4 is required for the activation of downstream signaling pathways. Thus, the receptor dimerization may be one of the first lines of regulation in activating TLR-mediated signaling pathways and induction of subsequent immune responses. Here, we report biochemical evidence that phytochemicals (curcumin and sesquiterpene lactone) with a structural motif that can confer Michael-type addition, inhibit both ligand-induced and ligand-independent dimerization of TLR4. These results imply that the activation of TLRs and subsequent immune/inflammatory responses induced by endogenous molecules or chronic infection can be modulated by certain dietary phytochemicals we consume daily.