To determine the role of Kruppel-like factor (KLF) 15, a zinc finger transcriptional factor that is expressed in vascular smooth muscle cells (VSMCs) in vascular biology. VSMCs respond to mechanical injury via a tightly orchestrated series of gene regulatory events. KLF15 is broadly expressed in both arterial and venous vascular beds in a VSMC restricted fashion. KLF15 expression is markedly reduced by both pharmacological and mechanical stimuli. To examine the specific role of KLF15 in the vascular response to injury, we performed femoral artery wire injury in KLF15^−/− and wild-type mice. KLF15^−/− mice develop exaggerated neointimal growth, with evidence of increased SMC proliferation and migration within the neointima. In concordance, gain and loss of function studies in isolated VSMCs demonstrate that KLF15 can directly inhibit SMC proliferation and migration. To our knowledge, these data are the first to identify KLF15 as a novel inhibitor of VSMC proliferation and migration and to implicate this factor as a critical regulator of the vascular response to injury.