The contractile tone of the vascular smooth muscle plays an important role on the regulation of the blood pressure as well as the local perfusion of the important organs such as the heart and brain. The importance of the Ca(2+) sensitivity in the regulation of the vascular tone has been established by the development of the simultaneous measurements of intracellular Ca(2+) concentration ( [Ca(2+)](i) ) and tension as well as that of the receptor coupled permeabilized preparation in the late 1980s. Recently, the mechanisms underlying the regulation of Ca(2+) sensitivity have been revealed. The increase in the Ca(2+) sensitivity involves the myosin phosphatase (MLCP) inhibition mediated by rhoA-rho kinase system and PKC-CPI system. The decrease in the Ca(2+) sensitivity involves the PKA-mediated inhibition of myosin light chain kinase, the PKG-mediated activation of MLCP, and PKA- or PKG-mediated inactivation of rhoA. In this article, the regulation of the Ca(2+) sensitivity of the contractile apparatus of the vascular smooth muscle will be briefly reviewed.