A new active rear steer (ARS) system has been developed. ARS is an electric four wheel steering system controlled by new logic(designed by H∞-μ synthesis) which maintains good control performance even if the vehicle parameters and /or road surface conditions are changed. ARS control is a typical technology to prevent vehicle side -slip in linear region of tire characteristic. This system offers easy control and reduces vehicle behavior of yawing motion before approaching critical limit. By combining ARS and vehicle stability control (VSC), it is possible to support driving precisely from normal driving to excessive driving. This paper describes the details of this new system which has been installed on 1997 model TOYOTA ARISTO for practical use in JAPAN.