A design method for regulators having poles in a specified region by using conformal mapping is proposed and the following two problems of regulator design are considered. The first is how to design all poles of a closed-loop system in a specified region by state feedback, and the other is how to design optimal regulators of which the poles may be located in a specified region, i.e. how to obtain the weighting matrices of a quadratic criterion function which yields all its poles in a specified disc with radius r and centre a within the left-half complex plane for continuous systems and in the unit circle for discrete systems.