Mixed lineage kinase domain-like protein （Mlkl） was recently found to interact with receptor interacting protein 3 （Rip3） and to be essential for tumor necrosis factor （TNF）-induced programmed necrosis （necroptosis） in cultured cell lines. We have generated Mlkl-deficient mice by transcription activator-like effector nucleases （TALENs）-mediated gene disruption and found Mlkl to be dispensable for normal mouse development as well as immune cell develop- ment. Mlkl-deficient mouse embryonic fibroblasts （MEFs） and macrophages both showed resistance to necrotic but not apoptotic stimuli. Mlkl-deficient MEFs and macrophages were indistinguishable from wild-type cells in their abil- ity to activate NF-KB, ERK, JNK, and p38 in response to TNF and lipopolysaccharides （LPS）, respectively. Consis- tently, Mlkl-deficient macrophages and mice exhibited normal interleukin-lp （IL-1β）, IL-6, and TNF production after LPS treatment. Mlkl deficiency protects mice from cerulean-induced acute pancreatitis, a necrosis-related disease, but has no effect on polymicrobial septic shock-induced animal death. Our results provide genetic evidence for the role of Mlkl in necroptosis.