Over two decades, the PI D (or fractional-order PID) controller was introduced and demonstrated to perform the better responses in comparison with the conventional integerorder PID controller. The PI D controller consists of five parameters, i.e. proportional gain (Kp), integration gain (Ki), derivative gain (Kd), integration order () and derivative order (). Effects of the PI D parameter tuning on the system responses are studied and summarized in this paper. Based on the modern optimization, designing the optimal PI D controller for an induction motor speed control system by using the cuckoo search (CS), one of the most efficient metaheuristic optimization search techniques, is proposed. Five parameters of the PI D controller will be optimized by the CS to meet the response specifications of the threephase induction motor (3-IM) speed control system which is defined as particularly constraint functions. Results obtained by the PI D controller are compared with those obtained by the conventional PID controller designed by Ziegler-Nichols tuning rule, Cohen-Coon tuning rule and the PI D controller designed by the CS. As simulation results, it was found that the PI D controller designed by the CS can provide faster and smoother speed responses than others, significantly. The stability of the 3-IM speed controlled system with the PI D controller designed by the CS is also investigated.