Disclosed are a biped walking robot, which carries out walking with a high energy efficiency through adjustment of the stiffnesses of joints of legs and improves walking stability through control of the pose of a torso, and a method of controlling the walking robot. The method includes generating a walking pattern of plural legs connected to a torso of the walking robot; adjusting stiffness of each of the plural legs interlocking with walking phases of the plural legs driven according to the walking pattern; and measuring a tilt of the torso, and compensating for the tilt of the torso such that the torso is parallel with the gravity direction.