Background: Mechanical ventilation of preterm lambs causes lung inflammation and injury to the airway epithelium, which is repaired by 15 days after ventilation. In mice, activated basal cells (p63+ KRT14+ KRT8+) initiate injury repair to the trachea, whereas club cells coordinate distal airway repair. In both human and sheep, basal cells line the pseudostratified airways to the distal bronchioles with club cells only present in terminal bronchioles. Hypothesis: Mechanical ventilation causes airway epithelial injury that is repaired through basal cell activation in the fetal lung. Methods: Ewes at 123±1 day GA had the head and chest of the fetus exteriorized and tracheostomy placed. With placental circulation intact, fetal lambs were mechanically ventilated with up to 15 mL/kg for 15 minutes, using 95% N2/5% CO2. Fetal lambs were returned to the uterus for up to 24 h. The trachea, left mainstem bronchi (LMSB), and peripheral lung were evaluated for epithelial injury and cellular response consistent with repair. Results: Peripheral lung tissue had inflammation, pro-inflammatory cytokine production, EGFR ligand up-regulation, increased p63 expression, and proliferation of pro-SPB, TTF-1 positive club cells. In bronchi, KRT14 and KRT8 mRNA increased without increases in Notch pathway mRNA or proliferation. In trachea, mRNA increased for Notch ligands, SPDEF and MUC5B, but not for basal cell markers. Conclusion: A brief period of mechanical ventilation causes differential epithelial activation between trachea, bronchi and peripheral lung. The repair mechanisms identified in adult mice occur at different levels of airway branching in fetal sheep with basal and club cell activation.