NADPH oxidase NOX4 is a source of reactive oxygen species in many tissue of human body. NOX4 products of activity are connected with various processes that take on the cellular and tissue level. One of them is cellular senescence. The role of this oxidase in the regulation of replicative and oncogene-induced senescence was shown in both normal and cancer cells. On the other hand NOX4 also stimulates to proliferation various types of cancer and primary cells, what promotes pathologies. NOX4 participates in epithelial-mesenchymal transition, important for tumor cells invasion and metastasis. Many research concern the role of NOX4 in the physiology and pathology of the cardiovascular system. It was shown that NOX4 has an impact on vasoconstriction, atherosclerosis development, vascular cells hypertrophy, apoptosis and differentiation. NOX4 plays both positive and negative role in the organism. Better understanding of NOX4 regulation and its involvement in signaling pathways give a hope to control the development of many diseases.