In the present study, TGF-β1 significantly increased levels of CDC27 in RLE-6TN cells, while hsa_circ_0044226 knockdown substantially reduced CDC27 expression in TGF-β1-treated RLE-6TN cells and in a mouse pulmonary fibrosis model, and those effects were largely reversed by exogenous expression of CDC27. This evidence concerns the gene TGFB1 and pulmonary fibrosis.