Argininosuccinate synthase 1 (ASS1) serves as a critical enzyme in arginine biosynthesis; however, its role in interstitial lung diseases, particularly idiopathic pulmonary fibrosis (IPF), re- mains largely unknown. This study aims at characterization and targeting of ASS1 deficiency in pulmonary fibrosis. We find that ASS1 was significantly decreased and inversely corre- lated with fibrotic status. Transcriptional downregulation of ASS1 was noted in fibroblastic foci of primary lung fibroblasts isolated from IPF patients. Genetic manipulations of ASS1 studies confirm that ASS1 expression inhibited fibroblast cell proliferation, migration, and invasion. We further show that the hepatocyte growth factor receptor (Met) receptor was acti- vated and acted upstream of the Src-STAT3 axis signaling in ASS1-knockdown fibroblasts. Interestingly, both arginine- free conditions and arginine deiminase treatment were demon- strated to kill fibrotic fibroblasts, attenuated bleomycin- induced pulmonary fibrosis in mice, as well as synergistically increased nintedanib efficacy. Our data suggest ASS1 deficiency as a druggable target and also provide a unique therapeutic strategy against pulmonary fibrosis.