For high speed magnetically levitated (MAGLEV) vehicle systems significant attention must be given to the secondary suspension as it determines the ride comfort and has great influence on the vehicle stabilty. This paper analyzes theoretically and experimentally the performance of an active secondary suspension on the ride quality and running stability of repulsive MAGLEV vehicles. The suspension is equipped with a microcomputer controlled pneumatic actuator and it is governed by an optimal control approach. Two measures of performance have been analyzed: car body vertical acceleration (ride comfort) and truck-guideway gap variations (running stability). The experimental results show the performance improvement obtainable with an active secondary suspension and sufficiently agree with the theoretical simulation. © 1992, The Japan Society of Mechanical Engineers. All rights reserved.