The Krüppel-like factors (KLFs) are a family of C2/H2 zinc finger DNA-binding proteins that are important in controlling developmental programs. Erythroid Krüppel-like factor (EKLF or KLF1) positively regulates the β-globin gene in definitive erythroid cells. KLF2 (LKLF) is closely related to EKLF and is expressed in erythroid cells. KLF2^-/- mice die between embryonic day 12.5 (E12.5) and E14.5, because of severe intraembryonic hemorrhaging. They also display growth retardation and anemia. We investigated the expression of the β-like globin genes in KLF2 knockout mice. Our results show that KLF2^-/- mice have a significant reduction of murine embryonic Ey- and βh1-globin but not ζ-globin gene expression in the E10.5 yolk sac, compared with wild-type mice. The expression of the adult β^maj- and β^min-globin genes is unaffected in the fetal livers of E12.5 embryos. In mice carrying the entire human globin locus, KLF2 also regulates the expression of the human embryonic ϵ-globin gene but not the adult β-globin gene, suggesting that this developmental-stage-specific role is evolutionarily conserved. KLF2 also plays a role in the maturation and/or stability of erythroid cells in the yolk sac. KLF2^-/- embryos have a significantly increased number of primitive erythroid cells undergoing apoptotic cell death. (Blood. 2005;106: 2566-2571)