It is important to regulate excessive inflammation when we treat patients with severe infectious disease. Sivelestat sodium hydrate (sivelestat), a neutrophil elastase inhibitor, is used in the treatment of lung injury but its effect on pneumonia is unknown. We examined the efficacy of sivelestat in combination with a fluoroquinolone, in a Legionella pneumophila pneumonia mouse model. The combination therapy did not show a significant survival improvement compared to the treatment with fluoroquinolone alone, but reduced bacteria number and inflammatory cells in the early phase. The combination therapy can contribute to treatment of L. pneumophila pneumonia with protecting lungs.