Vascular smooth muscle cells (VSMCs) form contractile layers around larger blood vessels in a process that is essential for the formation of a fully functional vasculature. Here, we show that integrin-linked kinase (ILK) is required for the formation of a unitary layer of aligned VSMCs around arterioles and the regulation of blood vessel constriction in mice. In the absence of ILK, activated Rho/ROCK signaling induces the elevated phosphorylation of myosin light chain leading to abnormally enhanced VSMC contraction in vitro and in vivo. Our findings identify ILK as a key component regulating vascular wall formation by negatively modulating VSMC contractility.