In this paper, a decoupling control for a non‐minimum phase system is considered in terms of the limiting form of linear optimal regulator problems, and an explicit relationship between the limiting properties and the decoupling control is shown. Moreover, using an appropriate performance index, this paper deals with a new method of decoupling control to exclude the effect of the fixed poles by pole‐zero cancellation. Stability and sensitivity are improved by this method. This paper also gives numerical examples to illustrate the effectiveness of decoupling control with the limiting form. © 2000 Scripta Technica, Electr Eng Jpn, 132(2): 49–57, 2000