The tuning of PID controllers is of great importance for process industries because it directly affects productivity, operability, and operating cost. Performance monitoring and maintenance of PID controllers are also serious issues for anyone seeking to maintain profitable plant operation. This paper presents a novel PID tuning methodology using a reference trajectory and a simple optimization-based algorithm. In particular, the proposed methodology is readily able to handle process constraints and to obtain PID tuning parameters using optimization directly. An application of this tuning method to a liquid level controller in a drum is shown, which has a constraint to avoid flooding of the liquid level. Furthermore, the method was implemented in DCSs of two kinds and was demonstrated successfully by simulation of a Crude Distillation Unit preflash drum.