A 22-year-old man was admitted to our hospital with fever, cough and dyspnea. His chest radiograph showed diffuse ground-glass attenuation in both lung fields. Arterial blood gas analysis showed hypoxemia (PaO2 28.7 Torr breathing room air) and he required mechanical ventilation within 6 hours after admission. Gomori methenamine silver (GMS) stain of the bronchoalveolar lavage (BAL) fluid smear showed round and indented organisms, and polymerase chain reaction revealed pneumocystis jirovecii in the BAL fluid. The HIV antibody was positive and peripheral blood CD4-positive lymphocytes decreased to 4.0%. Pneumocystis pneumonia complicated with acquired immunodeficiency syndrome (AIDS) was diagnosed. There was no four-fold rise in screen viral titers. We treated him with antibiotics, trimethoprim-sulfamethoxazole, ganciclovir, fos-fluconazole, steroid pulse therapy and sivelestat sodium hydrate. Respiratory failure was relieved within 5 days following treatment. The percentage of neutrophils in the BAL fluid was elevated (44.6%). Neutrophil elastase on admission was increased and improved to the normal range after treatment. Sivelestat sodium hydrate is an anti-neutrophil elastase inhibitor and may be one of the treatment options for acute respiratory failure due to pneumocystis pneumonia in AIDS patients.