The purpose of the present invention is to provide a novel treatment agent for pulmonary fibrosis for which there is currently no effective drug therapy established. The present invention is a therapeutic agent for pulmonary fibrosis containing mesenchymal stem cells. The pulmonary fibrosis is preferably usual interstitial pneumonia (UIP) or idiopathic pulmonary fibrosis (IPF). Also, the mesenchymal stem cells are preferably derived from adipose tissue or are allogeneic.
