Cell division cycle 25 A (Cdc25A), a dual-specificity protein phosphatase, is one of the most crucial cell cycle regulators, which removes the inhibitory phosphorylation in cyclin-dependent kinases (CDKs), such as CDK2, CDK4, and CDK6, and positively regulates the activities of CDKs that lead to cell cycle progression. In addition, Cdc25A also acts as a regulator of apoptosis. Overexpression of Cdc25A promotes tumorigenesis, and is frequently observed in various types of cancer. Here we briefly summarize current understanding of the role of Cdc25A in cell proliferation and apoptosis, as well as the impact of overexpression of Cdc25A on tumorigenesis.