Abstract: 【Abstract】 Objecitve To explore the block effect of brain-derived neurotrophic factor (BDNF) antibody on the mitogen extracellular kinase (MEK) expression in lung tissues of rats with brain ischemia. Methods Adult SD rats were divided into sham group, brain ischemia lung injury (BILI) group, and BDNF antibody treated group. Lung tissues were harvested at 3 days after operation. The distribution of MEK in the lung tissue was studied by immunhistochemistry, and the optical density values of MEK immunostaining was used to compare the difference of each group （n=5）. RT-PCR was used to determine the block effect of BDNF antibody on the level of MEK mRNA （n=8）. Results Immunohistochemistry showed that MEK immunoreactive positive products were observed in endothelia cells of airway and blood vessels. The optical density value in rats with brain ischemia significantly increased, compared with sham one (P<0.05). Moreover, BDNF antibody block could reverse this increase of BDNF immunostaining intensity (P<0.05). RT-PCR showed that BDNF antibody block significantly decreased the expressional level of MEK mRNA in the lung tissues with brain ischemia (P<0.05). Conclusion BDNF antibody block leads to a significant reduction of MEK expression in endothelia cells of lung tissue in the rats with brain ischemia.