Abstract: A magnetic-resistance control device for an exercise bicycle includes a platform connected with a base. A flywheel axle is rotatably mounted above the platform and is engaged with a rear wheel of the bicycle to rotate in an opposite direction thereof. A flywheel is made of magnetism-conducting material and is mounted to the flywheel axle for rotating therewith. A bracket is mounted on the platform. A U-shaped permanent magnet is slidably engaged on the bracket and defines an opening in which the flywheel is partly enclosed. The flywheel interacts with magnetic flux generated by the magnet when rotated such that a magnetic force is exerted on the flywheel, thereby generating a resistance to the flywheel. A driving device is provided for driving the magnet to reciprocate relative to the flywheel.