Due to its large deformation response to a low voltage, ionic polymer–metal composite(IPMC) is a highly attractive actuator for many applications in air or under water.However, the dynamic characteristics of IPMC are nonlinear and vary with time, especiallyin water actuations. In this study, a modified direct self-tuning regulator (DSTR) withintegral action was designed to control the tip-displacement of the IPMC, which is anon-minimum phase system to serve in air and underwater applications. The modifiedDSTR consisted of a pole-placement controller embedded with integral action, a referencemodel, and a self-tuning mechanism. The reference model specified the dynamiccharacteristic of the closed-loop IPMC system, and the controller parameters wereautomatically adjusted by the self-tuning mechanism to minimize the tracking error fromthe comparison between the response and the reference model output. The integral actionmay circumvent low-frequency distortions such as the back-relaxation phenomenon. Also,the DSTR may easily control the non-minimum phase system of the IPMC by tuning adelay factor in the reference model. The DSTR was implemented to control an IPMC (0.2 mm × 5 mm × 35 mm) actuated in air and under water, and the tracking performances were compared with aproportional-integral-derivative controller (PID). In contrast with the PID, theparameters of which were determined by the Ziegler–Nichols rule and produced largeroot-mean-squared tracking errors, the DSTR yielded good tracking performances foractuations both in air and under water from 0.01 to 1 Hz. Through control ofthe modified DSTR, IPMC may have a wide range of applications in the future.