Background: Pentose phosphate (PP) pathway is one of the major metabolic pathways associated with glucose metabolism. Glucose 6-phosphate dehydrogenase (G6PD) is a rate-limiting enzyme of PP pathway and its function is inhibited by 6-aminonicotinamide (6-AN). This study aims to investigate the role of the PP pathway in idiopathic pulmonary fibrosis (IPF). Methods: The metabolites of PP pathway were analyzed with Agilent 7890/5975 GC/MSD system and HP-5 MS column in the human lung tissues (IPF =31 and control=20). The roles of G6PD were evaluated using fibrotic markers in fibroblasts or epithelial cells treated with transforming growth factor-β1 (TGF-β1). The antifibrotic role of 6-AN was assessed in a bleomycin-induced lung fibrosis mice model. The levels of proteins in cell lysates or tissues were measured by western blot assays or RT-PCR. Results: The levels of PP pathway metabolites in IPF lung tissues were significantly elevated than those in control lung tissues. Moreover, protein expression of G6PD was increased in fibroblasts by TGF-β1 stimulation. 6-AN and G6PD specific siRNA reduced TGF-β1 induced mRNA or protein expression levels of collagen type-I and -SMA in fibroblasts. In addition, 6-AN decreased the TGF-β1 induced mRNA and protein expression levels of epithelial mesenchymal transition factor in Beas-2b cells. In bleomycin treated mice, 6-AN also decreased levels of hydroxyproline in the lung compared to that of control mice. Conclusions: Our findings indicate that inhibition of G6PD may have anti-fibrotic effects on pulmonary fibrosis, suggesting that G6PD is implicated as a potential therapeutic target in IPF.