Dietary flaxseed (FS) is a nutritional whole grain with high contents of omega-3 fatty acids and lignans with anti-inflammatory and antioxidant properties. We evaluated FS in a murine model of pulmonary ischemia/reperfusion injury (IRI) by dietary supplementation of 0% (control) or 10% (treatment) FS prior to IRI. Mice fed 0% FS undergoing IRI had a significant decrease in arterial oxygenation (PaO₂) and a significant increase in bronchoalveolar lavage (BAL) protein compared to sham operated mice. However, mice fed 10% FS undergoing IRI had a significant improvement in both PaO₂ and BAL protein compared to mice fed 0% FS undergoing IRI. Additionally, oxidative lung damage was decreased in 10% FS supplemented mice undergoing IRI, as assessed by malondialdehyde levels. Immunohistochemical staining of lungs for iPF₂-III F₂ isoprostane, a measure of lipid oxidation, was diminished. FS supplemented mice had less reactive oxygen species (ROS) release from the vascular endothelium in lungs in an ex vivo model of IRI, and alveolar macrophages isolated from FS fed mice had significantly reduced ROS generation in response to oxidative burst. Pulmonary microvascular endothelial cells produced less ROS in a flow cessation model of ischemia when preincubated with purified FS lignan metabolites. Pharmacologic inhibition of hemeoxygenase-1 (HO-1) resulted in only a partial reduction of FS protection in the same model. We conclude that dietary FS is protective against IRI in an experimental murine model, and FS affects ROS generation and ROS detoxification via pathways not limited to upregulation of antioxidant enzymes such as HO-1.