Despite recent progress in identifying a number of important factors that may play central roles in various renal diseases, the precise molecular basis of renal injuries remains unclear. Recent studies have documented an important role for oxidant stress in several renal diseases. Oxidant stress by overproduction of reactive oxygen species, generation of reactive nitrogen species, and/or modulation of cellular antioxidant enzyme activities, resulting in the activation of certain transcription factors, and synthesis and/or release of inflammatory cytokines, chemokines, growth factors, and extracellular matrix proteins. These changes alter the balance in the microenvironment of the kidney, and may activate signaling cascades that induce and propagate renal injury. Complex molecular interactions and cross-talk between the activated signaling pathways, in turn, define the nature and clinical course of the disease process. In this article, we will briefly present the relevance of the oxidant stress in the pathogenesis of various renal diseases.