Background <p>Bronchopulmonary dysplasia (BPD) is a major cause of morbidity and mortality in premature infants. Although gut microbial dysbiosis is implicated in BPD pathogenesis, the underlying mechanisms are poorly defined. This study aims to elucidate the specific pathway through which gut dysbiosis drives BPD pathology and to identify potential therapeutic targets.</p> Methods <p>The experimental BPD model was established by hyperoxia (FiO₂ 85%) in neonatal mice from postnatal days 1 to 14. Pulmonary alveolarization and inflammation were analyzed at postnatal day 15. The modulatory role of gut microbiota was assessed using antibiotic-induced dysbiosis and fecal microbiota transplantation (FMT) from normoxic mice. Gut microbiome analysis was performed using 16S rRNA gene sequencing. The specific signaling pathway was investigated using a pharmacological inhibitor of TLR4. Furthermore, the molecular mechanisms were investigated through western blotting, real-time quantitative PCR, ELISA, and immunofluorescence.</p> Results <p>Hyperoxia exposure induced impaired alveolarization, disrupted gut barrier integrity, and gut dysbiosis. These pathological changes were accompanied by elevated pulmonary inflammation, potent activation of the TLR4/NF-κB pathway, and upregulation of epithelial-mesenchymal transition (EMT) associated markers. These changes were exacerbated by early postnatal antibiotic administration, whereas FMT from normoxic mice rescued these phenotypes, restored gut barrier function, suppressed TLR4/NF-κB signaling, and reversed EMT progression. Notably, pharmacological inhibition of TLR4 mirrored the protective effects of FMT, effectively attenuating hyperoxia-induced lung injury and EMT.</p> Conclusions <p>Our findings establish a mechanistic link for the gut-lung axis in BPD, demonstrating that gut dysbiosis is a critical modulator of lung development impairment and pathological EMT via activation of the TLR4/NF-κB pathway.</p>