TLR4 is a member of the toll-like receptor family and can recognize lipopolysaccharide (LPS), the main component of gram-negative bacteria. To investigate how TLR4 responds to LPS, the TLR4 transcription levels in duck liver, spleen and bursa of Fabricius were examined after a model for immune stress was implemented through LPS injection in Peking ducks. The results from this assay suggested that LPS injection significantly increased the concentration of tumor necrosis factor-α (TNF-α) in bursa of Fabricius (P<0.05), along with an increase in the concentrations of immunoglobulin-G (IgG) and interleukin-12 (IL-12) in the serum of ducks at 1 day and 7 days after LPS injection (P<0.05). However, there were no apparent changes in organ index or the relative expression of TLR4 and IgM (P>0.05). Furthermore, correlation analysis showed a positive relationship between the mRNA expression of TLR4 and concentrations of TNF-α and IL-12. These results revealed that although there were no significant effects of LPS injection on TLR4 mRNA expression in lymphoid organs, the response to LPS may not mainly rely on the transcription of TLR4, and the downstream molecular response in the immune system may contribute more to the TLR4 signaling cascade.