Stability is the main requirement that must be met on the control system. If the plant from the control system is not stable, then the controller C can be searched so that the feedback system becomes internally stable. Let G be a transfer function represented by , where N, M are coprime factorization and element of family of all stable, proper, real rational function. Functions N and M can be found by using Euclidean algorithm and the state space method. Further, we find controller, that satisfy, NX + MY = I, so that the feedback system is internally stable. To verify the proposed method, numerical examples are given.