Motion control of biped robots includes a variety of tasks, such as controlling a robot walking on a horizontal plane, climbing stairs, moving on uneven surfaces, etc. This article describes modeling and designed control system for a biped robot standing on nonstationary plane. The problem of stabilization of the balancing robot, assembled on the basis of a robotic kit Bioloid, is considered for the case, when trajectories of movable plane are assumed to be bounded and unknown in advance. In contrast to previous works [4], [8] the mathematical model of the system is completed with dynamical equations and an estimator of nonstationary plane angle and angular velocity is designed. Performance of the proposed control algorithm is confirmed by numerical simulation. 978-1-4799-8701-6/15/$31.00 ©2015 IEEE.