Hypertrophic scar (HS) formation is associated with the fibrosis of fibrocytes caused by excessive extracellular matrix (ECM) synthesis and deposition, the initial event of HS formation. Our high throughput screen of miRNA expression profiles identified hsa-miR31–5p, whose transcription level was most differentially in normal skin fibroblasts (NS) and HS among other miRNAs. The level of hsa-miR31–5p in HS was significantly higher than in NS. In-vitro functional experiments showed hsa-miR31–5p knockdown remarkably suppressed the proliferation of hypertrophic scar fibroblasts (HSFBs) under hypoxia, promoted cell invasion, and inhibited the expression of Collagen I and III and Fibronectin (FN), suggesting that hsa-miR31–5p knockdown effectively reduces HS formation caused by excessive ECM synthesis and deposition in HSFBs under hypoxia. Mechanism study showed that the regulation of HS formation by hsa-miR31–5p was mediated by its target gene, factor-inhibiting HIF-1 (FIH): under hypoxia, hsa-miR31–5p down-regulated FIH and thus increased the level of hypoxia inducible factor-1α (HIF-1α), which subsequently activated the HIF-1α fibrosis regulation pathway in HSFBs, and stimulated the proliferation and ECM synthesis in HSFBs, eventually resulting in fibrosis and scar formation. The data also show that knockdown of hsa-miR31–5p in HSFBs impaired the trend of increased proliferation, reduced invasion and excessive ECM synthesis and deposition caused by HIF-1a activation under hypoxia through upregulating FIH, indicating that knockdown of hsa-miR31–5p effectively inhibits the formation of HS. In conclusion, hsa-miR31 -5p plays an important role in HS formation by inhibiting FIH and regulating the HIF-1α pathway. Therefore, hsa-miR31 -5p may be a novel therapeutic target for HS.