In our study, we found that transfection of HIF-1α-induced-miR-421 significantly down regulated the epithelial biomarker E-cadherin and up regulated N-cadherin, Fibronectin, Vimentin, Snail, Slug, Twist, MMP-2, and MMP-9 in cisplatin treated gastric cancer cell lines. The gene discussed is MMP9; the disease is gastric cancer.