Fibrosis occurs in systemic tissues other than the brain and finally induces dysfunction of the fibrotic organ. Kidney fibrosis is related to scarring after acute kidney injury and the progression of chronic kidney disease. Kidney function decreases with the progression of kidney fibrosis. As fibrotic tissue cannot return to its original status, advanced kidney fibrosis requires the administration of dialysis or kidney transplantation. Thus, elucidation the mechanism of kidney fibrosis is an important research theme. The proliferation and activation of (myo) fibroblasts and the excessive production of an extracellular matrix are common mechanisms in fibrosis in many organs, but it seems that kidney fibrosis has specific pathways. Tubular epithelial, mesangial cells, and erythropoietin producing cells, which exist only in the kidney, participate in forming kidney fibrosis. This review highlights an understanding of the cells and their underlying mechanisms, which are specific to kidney fibrosis process: transforming growth factor-β (TGF-β), epithelial-mesenchymal transition, wingless/int-1 (WNT) signaling, renal anemia, and uremia. Finally, we describe potential therapies that focus on the mechanisms of kidney fibrosis: anti-TGF-β antibody and mammalian target of rapamycin (mTOR).