Four pairs of binary mixtures of glass beads and iron powder were fluidized at various air velocities. The size of iron powder was constant at 180–212 ‍μm, while that of glass beads was varied to be 250–300 ‍μm, 300–355 ‍μm, 425–500 ‍μm and 610–700 ‍μm. It was found, in the four pairs, that glass beads (lighter particles, flotsam) move up and iron powder (heavier particles, jetsam) move down at middle ranged air velocities; density segregation appears regardless of the glass beads size. However, if the lower iron-powder-rich layers were investigated carefully for the pairs of 250–300 ‍μm and 300–355 ‍μm glass beads, the volume fraction of iron powder decreases with lowering the bed height, that is, the glass beads are captured in the lowest layer. On the other hand, the capturing of the glass beads does not occur in the pairs of 425–500 and 610–700 ‍μm glass beads. The origin of the glass beads capturing, and the reason of the presence or absence at different glass beads sizes were discussed considering the particles mobility at the interface between upper and lower layers, the particles packing structure of the lower layers, and the local air velocity at the lower layers.