A robot arm having a weight compensation mechanism. In one configuration, the robot arm includes a first link which is pivotably disposed, a first auxiliary link disposed parallel to the first link, a first pulley mounted on the first auxiliary link, a second pulley mounted on the first link, a wire connecting the first pulley to the second pulley, and an elastic member having one side mounted on the first link and the other side connected to the wire to provide an elastic force to compensate for the load of the first link.