MELK (Maternal Embryonic Leucine Zipper Kinase) is a serine/threonine protein kinase belonging to the AMPK (AMP-activated protein kinase) kinase family. It consists of a catalytic domain and a regulatory region, primarily localized in the cell nucleus and cytoplasm. MELK is involved in regulating various biological processes such as the cell cycle, self-renewal of stem cells, cell division, and apoptosis. By influencing different signaling pathways such as Wnt and Notch, MELK regulates cell fate determination. MELK is expressed in multiple tissues, especially in rapidly dividing cells such as cancer cells, and changes in its expression levels and activity are closely associated with tumorigenesis and tumor progression. Studies on specific gene expression and mutations have revealed the potential value of MELK in cancer therapy.