This paper presents a new PI tuning method for first order systems with a long dead time. The PI tuning rule is aimed to be simple so that it would be easy to design and apply the controller to industrial processes. The proposed tuning rule is found by z-domain design techniques, in order to get the fastest response without overshoot. The results obtained by the proposed method have been compared with other tuning rules like Ziegler-Nichols and Cohen-Coon, which are frequently used in actual practice. In addition to this, experimental results obtained by using the proposed PI tuning rule are also given.