This paper presents a novel quadruped robot, “Biodog II”, featuring low-inertia legs and coaxial transmission. Each leg has two degrees of freedoms (DOFs)-a knee and hip joint, which are actuated by proximal mounted DC motors, and a compliant ankle joint. Motor power can be transited to active joints efficiently and accurately by means of coaxial transmission. In particular, we employ a tendon-bone co-location structure on the leg to reduce stress and enhance strength. A Hopf oscillator-based Central Pattern Generator (CPG) is responsible for generating locomotion trajectories of different gaits. An embedded controller based on an ARM board is designed to command motors. Locomotion experiments including walk and trot gait test demonstrate the stability and mobility of Biodog II.