Magnetic forces acting on moving magnetic toners have been investigated by dropping the toners through dc and ac magnetic fields. A CCD camera system was used to observe the effects on magnetic toners in the magnetic fields. The distribution of toner chains in a dc magnetic field depends on the distribution of applied dc magnetic force. After applying an ac magnetic field greater than the coercivity of the toners, the length of toner chains was reduced and the sliding velocity of the toner chains was increased as the applied ac magnetic field was increased. The effects on magnetic toners by applying an ac magnetic field can be considered as an ac demagnetizing effect.