The present study aims to investigate the effects of toll-like receptor 4 (TLR4) antagonist in an ovalbumin (OVA)-induced mouse model of combined allergic rhinitis and asthma syndrome (CARAS). An OVA-induced mouse model of CARAS was established and TLR4 antagonist, TAK-242, was administrated intranasally or intraperitoneally. The number of sneezing and nasal rubbing was counted. The frequency of different cell types in the bronchoalveolar lavage fluid (BALF) and nasal lavage fluid (NLF) was analyzed using flow cytometry. Expressions of protein in nasal mucosa and lungs were determined using western blotting. Levels of interleukin (IL)-4, IL-5, and IL-13 were determined using Enzyme-linked Immunosorbent Assay (ELISA). Histological scores were applied for the assessment of lung injury. Treatment of TAK-242 downregulated CCL2 expression and reduced monocyte infiltration in nasal mucosa and lung tissues. Additionally, treatment of TAK-242 ameliorated upper airway symptoms including the sneezing and nasal rubbing by the regulation of cytokines including IL-4, IL-5, and IL-13. Furthermore, treatment of TAK-242 ameliorated lower airway symptoms including decreasing the frequency of CD45+SiglecF+CD11b+CD11c- eosinophils in BALF and IL13+ Th2 cells in the lungs. In conclusion, treatment of TAK-242 ameliorated CARAS-related lung injury by inhibiting lymphocyte infiltration, reducing monocytes infiltration, as well as regulating the frequency of eosinophils and Th2 cells.