TLR4-MD-2 complex plays a key role in LPS recognition and its signal transduction. These steps are the vital elements of the host’s defensive reaction. Studying the functional domain of TLR4 and MD-2 is very important to further understand the mechanism of LPS signal transduction. It was studied the interaction domain of TLR4 and MD-2 in living cells based on gene mutation, gene transfection and fluorescence resonance energy tramsfer(FRET) which is considered as one of the best methods used for intracellular protein-protein interaction study. CY-15P which was fused by CFP and YFP through 15 neutral amino acids was used as positive control, while co-expressed CFP and YFP proteins were used as negative control. The results showed that the ability of TLR4 binding to MD-2 decreased dramatically after the deletion of Glu²⁴～Met⁴¹ in N terminal of TLR4. Aggregation of TLR4 to LPS stimulation was observed, however, TLR4 without the Glu²⁴～Met⁴¹ mutation did not aggregate. All these results indicated that TLR4 Glu²⁴～Met⁴¹ might be the interaction domain of TLR4 binding to MD-2 and participate in the aggregation effect of TLR4 upon LPS stimulation.