STAT3-IN-39 (compound 10K) is an orally active STAT3 inhibitor that exhibits excellent inhibitory activity against STAT3 phosphorylation, with an IC 50 of 0.47 μM in NIH-3T3 cells. STAT3-IN-39 inhibits the TGF-β1-induced fibrotic response and blocks the epithelial-mesenchymal transition in A549. STAT3-IN-39 can be utilized in research related to idiopathic pulmonary fibrosis.