A rehabilitation exoskeleton with physiotherapists in their everyday using routine is gradually becoming the normal case. The Active Disturbance Rejection Controller (ADRC) is used in this article to control the proper execution of fundamental limb rehabilitation trainings. The experiment is carried out on a flexible single joint exoskeleton model, whose behavior is similar to that of a real robotic rehabilitation equipment. In this study, we used two ADRC configurations and compared their robustness to external and internal disturbances with uncertainty in system parameters, these classical or linear (LADRC) and optimized fractional ADRC (FADRC). According to the root mean square error (R.M.S.E) as a performance index tool, the results reveal that (FADRC) appears to be better than (LADRC).Matlab and the Simulink tools were used to create all simulation results.