The preview control problem is one in which a controller can use future information as well as present and past information in deciding the control. In this paper the application of optimal preview control to an active suspension system for railway vehicles is discussed. Since many vehicles pass on the same railline repeatedly, preview control is an applicable for its active suspension. The results of simulations and experiments which are performed for optimal preview control system and for a conventional LQ control system show that optimal preview control improves ride quality drastically and reduces energy spent for control. Furthermore, identification of disturbance is also studied.