Pluripotency of embryonic stem (ES) cells is maintained by a network consisting of multiple transcription factors, including Oct3/4, Sox2, Nanog, Klf4 and Sall4. Among these factors, the forced expressions of Oct3/4, Sox2 and Klf4 are sufficient to reprogram fibroblasts into induced pluripotent stem (iPS) cells. The current study analyzed the role of Sall4 during the generation of ES cells and iPS cells. The mouseSall4gene was deleted by homologous recombination. Sall4-null embryos died shortly after implantation, as has been reported. ES-like cell lines can be established from Sall4-null blastocysts, albeit with a lower efficiency and a slower time course. The knockdown ofSall4significantly decreased the efficiency of iPS cell generation from mouse fibroblasts. Furthermore, retroviral transduction ofSall4significantly increased the efficiency of iPS cell generation in mouse and some human fibroblast lines. These results demonstrated that Sall4 plays positive roles in the generation of pluripotent stem cells from blastocysts and fibroblasts.