Skin fibrosis is a common pathological process characterized by fibroblast proliferation and excessive deposition of extracellular matrix. However, the pathogenesis of the disease is still not clear. Previous studies have shown that microRNA-21 may play pivotal roles in the regulation of a variety of skin fibrosis, including keloid, scleroderma, and hypertrophic scar. In this review, we outline the structure, expression, and regulation of microRNA-21 and its role in fibrotic skin diseases. In future, it may be useful as a prognostic or diagnostic marker. However, there is a significant amount of work required to increase our current understanding of the role of microRNA-21 in skin fibrosis.