Abstract: In this paper, a nonlinear PID controller is studied based on “proportional component approach” (called “NPID-PCA”). While compatible with the conventional PID technique, this type of controllers imposes three independent nonlinear functions between the proportional forces on the error signals to synthesize nonlinear PID controllers. Due to its simplest characteristics in nonlinear proportional forces, the proposed controller provides a better means for designing and tuning of controller′s nonlinearity. A spline-based function is adopted to realize the nonlinear functions with a graphical interface. Several examples are given in comparison with the other existing nonlinear PID controllers. Simulation results confirm the superior performances of the proposed controllers for plants with time delay or dead zone. The toolbox of NPID-PCA has appeared to the public as “open source” software.