Blepharophimosis, ptosis, epicanthus inversus syndrome (BPES) is an autosomal dominant genetic disorder characterized by small palpebral fissures and other craniofacial malformations, often with (type I) but could also without (type II) premature ovarian failure. While mutations of the forkhead transcription factorFOXL2are associated with and likely be responsible for many BPES cases, howFOXL2affects craniofacial development remain to be understood. Through a large-scalepiggyBac(PB) insertion mutagenesis, we have identified a mouse mutant carrying aPBinsertion ˜160 kb upstream of the transcription start site (TSS) ofFoxl2. The insertion reduces, but not eliminates, the expression ofFoxl2. This mutant, but not its revertant, displays BPES-like conditions such as midface hypoplasia, eyelid abnormalities and female subfertility. Further analysis indicates that the mutation does not affect mandible, but causes premature fusion of the premaxilla-maxilla suture, smaller premaxilla and malformed maxilla during midface development. We further identified an evolutionarily conserved fragment near the insertion site and observed enhancer activity of this element in tissue culture cells. Analyses using DNase I hypersensitivity assay and chromosome conformation capture assay in developing maxillary and periocular tissues suggest that the DNA region near the insertion site likely interacts withFoxl2TSS. Therefore, this mutant presents an excellent animal model for mechanistic study of BPES and regulation ofFoxl2.