Design, control and evaluation of a lower limb wearable robotic exoskeleton for power assistance are presented in the paper. The proposed four degree-of-freedom robotic exoskeleton, an active flexion/extension and a passive abduction/adduction rotation at each hip joint, is characterized with complying with the swinging motion of lower limbs as close as possible. To perform power assistance on walking, the linear extended state observer (LESO) based controllers were designed for the walking assistance. Finally, the experiments were conducted to validate the prototype of lower limb robotic exoskeleton. The associated evaluations for the walking assistance were also investigated using the motion captured system and EMG signal.