Objective To compare the changes in TLR4-NF-κB signaling pathway in infant and adult mice infected with influenza virus, and to provide experimental evidence for the study of immunopathological mechanism in pediatric respiratory virus susceptibility. Methods Immunohistochemistry and RT-PCR were applied to detect the expressions of lung TLR4 and NF-κB P65 mRNA and proteins in the infant and adult mice, and to compare the changes in TLR4-NF-κB P65 signaling pathway after infection with influenza virus. Results(1) The infant model group showed the strongest expression of TLR4 protein in the lung tissue, compared with that in the normal group and adult model group showing significant differences(P<0.05).(2) The expression of NF-κB P65 protein in the lung tissue was strongest in the infant model group, and it was gradually increased over time, showing a significant difference between each time point and the next time point(P<0.05).(3) The infant model group showed the strongest expression of TLR4 mRNA in lung tissue, significantly higher than that in the normal and adult model groups(P<0.05).(4) The expression of NF-κB P65 mRNA in the lung tissue was highest in the infant model group, and significantly higher than that in the normal and the adult model groups(P<0.05), and it was gradually increased with the time. Conclusions The over-activation of TLR4-NF-κB P65 signaling pathway may be one of the immunopathological mechanisms of serious injury in the lung tissue in infant rats.