A biomimetic compensating controller designed to increase prosthetic hand grip force, based on wrist rotational acceleration, is developed and experimentally evaluated. Wrist acceleration can cause objects in grasp to slip. A sliding mode controller is implemented and experimentally evaluated for a prosthetic wrist rotator. Experimental results indicate that the biomimetic grip force compensation controller decreases the likelihood of object slip. For the wrist rotator, experimental results demonstrate that sliding mode control is effective for smooth velocity control, due to robustness to nonlinearities.