Objective Observing the expressions of inducible nitric oxide synthase （iNOS） and endothelial nitric oxide synthase （eNOS） mRNA in lung tissues of rats with acute necrotizing pancreatitis （ANP） to explore the role of NOS in ANP associated-lung injury. Methods Forty Wistar rats were assigned into ANP group (n=30) and sham-operation group (SO group, n=10). ANP model was induced by retrograde injection of 5% sodium taurocholate into the bili-pancreatic duct. Pathological changes of the lung tissue were observed under light microscope at 3 h, 6 h and 12 h after the ANP-model operation, and the expressions of iNOS mRNA and eNOS mRNA in lung tissue were assayed by RT-PCR. Results Different degrees of pathological changes of the lung tissue, such as hyperemia, edema, inflammatory cells infiltration, hemorrhage and necrosis, were found in the ANP group. The pathologic injury scores of lung tissue in ANP group were higher than that in SO group (Plt;0.05), and gradually increased with the duration extension of ANP (Plt;0.05). Compared with the SO group, the expressions of iNOS and eNOS mRNA in ANP group were all higher at 3 h, 6 h, and 12 h (Plt;0.05). Conclusions The overexpressions of iNOS and eNOS mRNA may play important roles in lung injury of ANP. This provides us a theory basis that lung injury of ANP could be relieved by inhibiting the expressions of iNOS and eNOS mRNA.