To clarify the effects of anticoagulant therapy, we investigated patients with rapidly progressive interstitial pneumonias, retrospectively. We defined rapidly progressive pneumonia as idiopathic or secondary interstitial pneumonia with acute exacerbation of respiratory symptoms within 2 months, without infection or heart failure. A total of 20 cases admitted to our hospital between April 1999 and January 2010 met our criteria. Of those 20 cases, 6 were non-idiopathic pulmonary fibrosis (non-IPF), 3 were IPF, 6 were amyopathic dermatomyositis (ADM), 2 were DM, 2 were rheumatoid arthritis, and 1 was mixed connective-tissue disease. We divided the 20 cases into two groups according to whether they were treated with anticoagulant therapy (dalteparin and/or warfarin) (group A, n = 11) or not (group B, n = 9), and compared their outcomes. They were all given standard therapy. There was significantly better survival time in group A than in group B by the Kaplan-Meier survival curve (p = 0.0389). Anticoagulant therapy may improve the survival of patients with rapidly progressive interstitial pneumonias.