Intrafascicular Microelectrode Stimulation (IMS) provides potentially advantageous methods for restoring motor function in patients with spinal cord injuries. One goal of IMS is to provide precise muscular force control. To this end, force-feedback, closed-loop IMS methods were investigated for submaximal isometric force control of an isolated feline medial gastrocnemius muscle. A dSPACE® real-time control system was used to provide pulse-width-modulated current to a single intrafascicular electrode on a Utah Slanted Electrode Array, which was implanted in the sciatic nerve. A proportional plus integral (PI) error-based controller, along with feedforward pulse-width estimation (FPWE), was evaluated for a step input of 21-N over a 10-s interval. This controller performed on-line adjustments to the pulse width of the delivered stimulus, on the basis of discrepancies between the target force and the actual force being generated, in order to reduce the error. Electrical stimulation of motor nerves generally elicits a fast-rising muscular force response that shows an initial potentiation (gradual rise in force, to above the target force level), followed by fatigue (decline in force, to below the target force level). As expected, responses on open-loop FPWE trials demonstrated high potentiation along with high fatigue in this experiment. In comparison, as a consequence of on-line, error-based adjustments to stimulus pulse widths, responses on closed-loop PI controller trials exhibited substantially less potentiation and fatigue, and reached the target force faster. The ability of a proportional (P) error-based controller, along with a perithreshold FPWE, to track a 10-s, 0.5-Hz, 1-to-11-N sinusoidal force trajectory was also examined. The closed-loop P control system with perithreshold FPWE successfully followed the variable force trajectory with low error and low phase delay. Thus, the closed-loop IMS control methods used in this experiment were beneficial for both 1) rapidly achieving and maintaining a static, submaximal, isometric force, and 2) accurately tracking a variable, submaximal, isometric force trajectory. These results suggest that similar closed-loop IMS force control methods can be developed for human patients in order to restore motor function.