Abstract: Owing to large amount of computational labour,the LQG self-tuning controllershave not been used widely in spite of its many advantages.A new self-tuning controller based on optimal control and input-output plant model is presented,where thesolution of the Riccati equation and spectral factorization are not required.The algorithm is easy to implement and requires less computational labour than previous LQG self-tunners do.Analysis of some closed-loop properties is given in the paper.Simu-lation results demonstrate that this version of self-tuning controller possesses all theadvantages of an ordinary LQG control.