Objective To investigate the effect of Piezo1 activated by mechanical stress on knee osteoarthritis synovial fibrosis via the extracellular signal-regulated kinase (ERK)1/2 signaling pathway. Methods Twenty-five Sprague Dawley rats were divided into blank, exercise, exercise+GsMTx4, exercise+PD98059, and exercise+GsMTx4+PD98059 groups (n=5 per group). After modeling, serum and synovial tissue were extracted and collagen deposition was evaluated by Sirius red and Masson staining. Expression levels of Piezo1, ERK1/2, phospho (p)-ERK1/2, α-smooth muscle actin (SMA), transforming growth factor (TGF)-β, Collagen I, and tissue inhibitor of metalloproteinase (TIMP)-1 were detected by Western blot and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and the interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α contents were detected by enzyme-linked immunosorbent assay. For cell experiments, synovial cells were divided into blank, pull, pull+GsMTx4, pull+PD98059, and pull+GsMTx4+PD98059 groups and the above indices were detected in the model cells by Western blot, RT-qPCR, and other techniques. Results Mechanical stress increased collagen deposition in synovial tissues in the rats, and increased the protein and mRNA expression levels of the pathway-related and fibrosis-specific indicators Piezo1, p-ERK/ERK, α-SMA, TGF-β, Collagen I, and TIMP-1 (P<0.05). Piezo1 expression was significantly down-regulated by both inhibitors (P<0.05), but the ERK inhibitor (PD98059) had no significant effect on Piezo1 gene expression. Levels of serum inflammatory factors were significantly higher in the exercise group compared with the blank group (P<0.05), and levels were significantly reduced by the inhibitors (P<0.05). The in vitro experiments showed the same trends as the animal experiments. Conclusions The Piezo1 ion channel can sense mechanical stress and activate the ERK1/2 pathway to mediate knee synovial fibrosis.