This paper presents a robust motion control of a sitting-type lower limb rehabilitation robot (LLRR) in its operational-space. The mathematical background of the proposed robot is discussed and its motion control design in the task-space based on a double-loop control approach is derived herein along with its closed-loop system stability analysis. The motion tracking performance analysis of the proposed scheme is demonstrated using computer based numerical simulations. For numerical simulations and to validate the effectiveness of the motion control strategy, the clinically obtained test gait data is used for the desired motion trajectory of the lower limb rehabilitation robot. © 2020, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG.