Abstract: DEC1 is a basic helix-loop-helix(bHLH)transcription factor involved in the regulation of cell proliferation, cell differentiation, lymphocytes maturation, circadian rhythms, immune response and response to hypoxia. Recent studies have revealed that the expression of DEC1 is abnormally high in various tumor tissues and cells. In addition, the expression of DEC1 in the tumor tissue is related to the malignancy of various cancer types. This paper, therefore, focuses on the relationship between DEC1 and proliferation, apoptosis, cellular senescence, invasion and metastasis of tumor cells, in order to elaborate the role of DEC1 in the pathogenesis and progression of tumor.