SALL4, a human homolog to Drosophila spalt, is a novel zinc finger transcriptional factor essential for development. We cloned SALL4 and its isoforms (SALL4A and SALL4B). Through immunohistochemistry and real-time reverse-transcription-polymerase chain reaction (RT-PCR), we demonstrated that SALL4 was constitutively expressed in human primary acute myeloid leukemia (AML, n = 81), and directly tested the leukemogenic potential of constitutive expression of SALL4 in a murine model. SALL4B transgenic mice developed myelodysplastic syndrome (MDS)-like features and subsequently AML that was transplantable. Increased apoptosis associated with dysmyelopoiesis was evident in transgenic mouse marrow and colony-formation (CFU) assays. Both isoforms could bind to β-catenin and synergistically enhanced the Wnt/β-catenin signaling pathway. Our data suggest that the constitutive expression of SALL4 causes MDS/AML, most likely through the Wnt/β-catenin pathway. Our murine model provides a useful platform to study human MDS/AML transformation, as well as the Wnt/β-catenin pathway's role in the pathogenesis of leukemia stem cells.