Background <p>Renal fibrosis is a major pathological feature in chronic kidney disease, and is considered the final common pathway for virtually all progressive kidney diseases. Although a large amount of progress has been made in understanding renal fibrosis, the pathogenesis is very complex and still incompletely understood.</p> Methods <p>Renal fibrosis was induced by unilateral renal ischemia–reperfusion (uIR) operation. In some experiments, microRNA-145b (miR-145b) mimic or locked nucleic-acid-modified (LNA-modified) anti-miR-145b was delivered to mice through tail vein injection every 2&#xa0;days, for a total of seven injections following uIR operation. In some experiments, YC-1 (a selective HIF-1α inhibitor) was given intraperitoneally on the day of uIR operation and continued until the mice were euthanized. The mice were euthanized 2&#xa0;weeks after uIR operation for further analysis.</p> Results <p>We demonstrated a significant increase of microRNA-145b (miR-145b) in renal tubular cells in mice following a uIR operation. The uIR operation led to the activation of HIF-1α in renal tubular cells, and inhibition of HIF-1α prevented the increase of miR-145b. Chromatin immunoprecipitation (ChIP) assays further verified HIF-1α directly binding to the miR-145b gene promoter upon uIR operation. Functionally, inhibiting miR-145b using locked nucleic-acid-modified (LNA-modified) anti-miR-145b could aggravate renal tubular injury and promote the progression of renal fibrosis following uIR operation, indicating that miR-145b serves as an anti-fibrotic factor. Further, our study also found miR-145b in vivo transfection suppressed the expression of angiopoietin-2 (Angpt2) in mice after uIR operation. Luciferase microRNA target reporter assays further verified Angpt2 as a direct target of miR-145b.</p> Conclusions <p>This study unveiled a HIF-1α/microRNA-145b/Angpt2 axis that could ameliorate tubular injury and delay the development and progression of renal fibrosis.</p>