An exoskeleton robot is an external structural mechanism with Joints and links corresponding to those of the human body. When it is worn, it transmits torques from actuators through rigid exoskeletal links to the human Joints. We have been developing exoskeleton robots for assisting the motions of physically weak persons such as elderly or disabled in dally life. In this paper, we propose an electromyogram (EMG) based control (i.e., control based on the skin surface EMG signais of the user) for the exoskeleton robot to assist physically weak person's lower-limb motions. The skin surface EMG signals are mainly used as the input information for the controller. In order to generate flexible and smooth motions and take into account the changing EMG signal levels according to the physical and psychological conditions of the user, fuzzy-neuro control method has been applied for the controller. The experimental results show the effectiveness of the designed EMG-based controller for the power-assist.