Separation of Silicastone and pyrophyllite due to density difference with a gas-solid fluidized bed is investigated. We employ mixtures of glass beads and steel shots with various mixing ratios as a fluidized medium to obtain fluidized beds of various bulk densities. Floating and sinking of the ores in the fluidized bed are examined by changing the bulk density and the superficial velocity. It is found that the separation of two ores with a slight density difference is possible at a high separation efficiency by careful adjustment of the mixing ratio. The separation efficiency depends on the superficial velocity because it alters the flow patterns of particles and bubbles in the fluidized bed, which affect the floating and sinking of the ores.