The serine/threonine protein kinase Rho kinase, a downstream effector of the small GTPase Rho, regulates actin cytoskeletal organization, cell adhesion, cell motility, smooth muscle contraction and gene expression. Rho kinase constitutes the essential regulatory system for myosin phosphatase, controlling myosin light chain phosphorylation and thereby vascular tone. Inhibitors of Rho kinase were shown to be effective in ameliorating hypertension, vasospasm, vascular injury and associated organ damages in various animal disease models. These recent observations imply potential usefulness of the Rho kinase inhibitors as novel therapeutic and preventive agents for vascular disorders and accompanying organ injury.