Abstract: Nanog is a key transcription factor involved in maintaining the self-renewal and pluripotency of embryonic stem cells. The expression of Nanog is gradually decreased with cell differentiation and tissue maturation. The recent studies demonstrate that Nanog expression is restored in tumor cells. Nanog plays pleiotropic roles in tumorigenesis and tumor development. Nanog promotes tumor growth, metastasis and drug resistance via regulating tumor cell proliferation, migration and invasion, tumor stemness, as well as tumor immune escape. Nanog overexpression is an independent indicator for poor prognosis. In this review, we summarize the recent progress of Nanog in tumor and the underlying molecular mechanisms, with an emphasis on the potential of Nanog in tumor diagnosis and targeted therapy.