Objectives: To study the efficacy and safety of intravenous pulse Cyclophosphamide therapy (six times every 4 weeks) in combination with Glucocorticoid for interstitial pneumonia in dermatomyositis. Subjects: 41 dermatomyositis patients, diagnosed by 1995 Tanimoto criteria, with interstitial pneumonia, hospitalized in Rheumatology Department, Bach Mai hospital from May 2008 to October 2011. Methods: longitudinal follow-up study of therapeutic intervention. Results: Respiratory symptoms were improved: cough with phlegm (58.5 percent in T0 compared with 12.2 percent in T6) and rales in lung (97.6 percent in T0 compared with 31.7 percent in T6). Pulmonary function test showed clearly improvement but lesions in X ray and computed tomography were less changes. There was neither death nor severe toxicities observed. Conclusions: As for interstitial pneumonia in dermatomyositis patients, intravenous pulse cyclophosphamide therapy improved clinical symptoms but lesions in X-ray and CT were less changes. This is a safe therapy.