Rationale: Surfactant Protein D (SP-D) is a member of the collectin family of soluble, innate host defense molecules with demonstrated immunomodulatory properties in vitro. Constitutive absence of SP-D in mice is associated with lung inflammation, alteration in surfactant lipid homeostasis, and increased oxidative-nitrative stress. Objectives: To test the hypothesis that SP-D would protect against acute lung injury from hyperoxia in vivo. Methods: Transgenic mice overexpressing rat SP-D either constitutively (SP-D OE) or conditionally via regulation with doxycycline (SP-D Dox-on) were each subjected to continuous hyperoxic challenge for up to 14 days. Results: Compared to littermate controls (WT), SP-D OE mice exposed to 80% O₂ demonstrated substantially increased survival accompanied by significant reductions in wet to dry lung ratios and BAL protein. Although SP-D OE and WT mice each exhibited a 2-fold increase in total BAL cells and neutrophilia in response to hyperoxia, the SP-D OE group had lower levels of BAL pro-inflammatory cytokines and chemokines including IL-6, TNF-, and MCP-1, increased mRNA levels of the transcription factor Nrf-2 and phase 2 antioxidants HO-1, GPx-2 and Nqo1 and decreases in lung tissue thiobarbituric-acid reactive substances. As proof of principle, the protective role of SP-D on hyperoxic injury was confirmed as SP-D Dox-on mice exposed to 85% O₂ demonstrated increased mortality upon withdrawal of doxycycline. Conclusions: Local expression of SP-D protects against hyperoxic lung injury through modulation of pro-inflammatory cytokines and antioxidant enzymatic scavenger systems.