Legged robots are much difficult to design and control than wheeled robots. However, one of advantages of the legged robots is that they are move adaptable to rough terrains and the task of stepping over obstacles. The gait algorithm of a robot is an important job before components the configuration of the body and each leg. The main purpose of this thesis is to discuss leg failure in gait planning procedure for multi-legged robots with symmetric structures. The legs discussed herein are in the form of an articulated arm with three revolute joints. Various effects on motion characteristics due to different leg faults, such as robot¡¦s walking efficiency and stability are also investigated. On extreme conditions, the robot will cease to walk after a leg failure. In this work a scheme is proposed to transform the scrambled leg pattern to a better or even optimum configuration. This leg switching scheme can improve the stability of the robot when problematic legs are disconnected from the body.